The first time I served this chocolate zucchini cake, I didn’t tell anyone there was zucchini in it. When I finally mentioned the four and a half cups of grated zucchini hiding in the crumb, the response was “where?!” and “make this for my birthday.” That’s the thing about chocolate zucchini cake: when done right, the zucchini doesn’t read as a vegetable at all. It simply serves as moisture, and with the chocolate, it turns fudgy.
Most zucchini cakes I’ve eaten over the years fail in two ways. They’re either dry and a bit bland (the cocoa pulled too much moisture, the zucchini was wrung out, the cake was overbaked), or they’re soggy and dense (too much zucchini with no structural compensation, so the cake is gummy in the middle). My version is built specifically to avoid those two failures. It uses sour cream, vegetable oil, and grated zucchini, balanced with enough flour, eggs, and a generous amount of cocoa. The result is fudgy without being heavy, moist without being wet, and rich enough that nobody’s asking what the green flecks were.
This is a three-layer celebration cake, not a snack cake or a sheet cake (though there are variations given below). The buttercream is built around a chocolate ganache, which gives it a glossier, deeper chocolate character than buttercream made with cocoa alone. I recently updated this recipe post from the original one published in 2019. The cake recipe itself is the same! I have added more tips and answered some reader questions throughout the post to help you bake the best cake.
A reader, Michelle, says: “I made this cake yesterday and it was off the charts! The zucchini is undetectable, and the chocolate chips add an element of surprise! It is decadent and moist. The buttercream is not too sweet. Your recipes and tutorials have inspired me to start baking and have now discovered a new passion! Thank you, John!!” ★★★★★
Table of Contents
Why This Recipe Works
There are three things that make this cake what it is, and all three are doing structural work—they aren’t there for flavor alone.
Cocoa powder is hygroscopic, so the recipe is built around moisture. Cocoa powder has a remarkable thirst. It pulls moisture from the surrounding batter as it hydrates, which is why cocoa-heavy cakes have a reputation for ending up dry. The fix isn’t less cocoa (we want the rich chocolate flavor); it’s more moisture. This recipe uses 1½ cups of vegetable oil, ½ cup of sour cream, and 4½ cups of grated zucchini specifically to balance the cocoa’s drying effect. Take any of those three away, and the cake drops a tier in tenderness and moistness.
Zucchini contributes water without flavor. What zucchini actually does in a cake is donate its very high water content (about 95% by weight) to the crumb during baking. That moisture stays in the cake even after the structure sets, which is why zucchini cakes hold their tenderness for days, while a plain chocolate cake can dry out in 24 hours. The zucchini itself disappears. The cell walls collapse during baking, the chlorophyll-bearing skin cells break down to dark specks almost indistinguishable from the chocolate, and the only thing left to suggest there’s a vegetable involved is the texture. Which, honestly, is hardly even noticeable, and the chocolate chips add texture, so you really only focus on those.
The buttercream uses melted chocolate as well as cocoa powder. Most chocolate buttercream recipes rely on cocoa powder alone, which gives chocolate flavor but a slightly powdery character. This frosting starts with chocolate chips melted into heavy cream to make a soft ganache. Cocoa powder goes in too for additional flavor. The two combined result in a deeply chocolaty frosting with the silky, glossy feel of ganache but the pipeable structure of American buttercream.
Ingredients You’ll Need
These are the main ingredients you need to make this decadent chocolate zucchini cake recipe. You can find the full list of ingredients and measurements in the recipe card below.
All-purpose flour — measured by spoon-and-level or by weight. Adding too much flour is the single most common reason a cake ends up dry, and cocoa cakes show that mistake faster than vanilla cakes do.
Unsweetened natural cocoa powder — natural, not Dutch-processed. Natural cocoa is acidic, which reacts with the baking soda for lift. If you only have Dutch-processed, you’d need to swap baking soda for baking powder in the right ratio, and the cake will taste slightly less assertive in chocolate flavor.
Espresso powder — does not make the cake taste like coffee. Espresso amplifies chocolate flavor by adding bitterness compounds that sit alongside the cocoa flavor compounds. The difference with vs. without is meaningful, but the cake still works without it. I made this twice last summer, once with espresso powder and once without, and served slices side-by-side to my husband without telling him which was which. He picked the espresso-powder version both times as ‘more chocolatey’ without knowing why.
Vegetable oil — neutral oil. Oil rather than butter because oil is liquid at room temperature, which means the cake stays soft and tender at room temperature instead of going firm the way butter cakes do. Canola or grapeseed works identically.
Sugar — you will use three types in this recipe: granulated sugar and brown sugar for the cake batter, and powdered sugar for the buttercream. Brown sugar contributes a molasses flavor that pairs with cocoa, plus the extra moisture and slight acidity from the molasses help the chemical leaveners along. Powdered sugar sweetens and stiffens the frosting for the perfect balance of fudginess and structure to hold the cake layers together.
Large eggs, room temperature — the high egg count is what holds 4½ cups of zucchini and other ingredients together in a structurally coherent cake; with fewer eggs, the cake collapses under the moisture load.
Sour cream — the acid in full-fat sour cream activates the baking soda, while the fat enriches the crumb. Plain full-fat Greek yogurt works as a swap.
Grated zucchini — will will 2-3 whole zucchinis, depending on their size. Measure them whole at the store and aim for a total weight of at least 500g to account for some loss of the stem end when you grate them.
Semi-sweet chocolate chips — you will fold some into the batter. They melt during baking into pockets of fudge. The rest is used to make the ganache as the base of the buttercream.
Unsalted butter — essential for the smoothness of the frosting. Be sure to set your butter sticks out with enough time for them to soften. If you’re short on time, you can use one of my hacks to soften butter in 10 minutes or less.
Should You Squeeze The Zucchini? (The Honest Answer)
This is the question I answer on every baking recipe that uses zucchini, and the food world is genuinely split on it. Some recipes call for wringing the zucchini hard in a kitchen towel. Others insist you should never squeeze it. After making this recipe more times than I can count, here’s what I’ve actually concluded:
For my chocolate zucchini cake, the answer is no. If you squeeze out the moisture from the zucchini, you risk making the cake dry and dense. Some advice says that it depends on the zucchini, whether it’s fresh from your garden or older and larger from the grocery store. But that is dependent on so many factors, and the reality is, most of us are picking up a zucchini or two when we’re doing our weekly grocery run. (I do use the zucchini in my garden for baking, and have great results!)
Here’s what to do in practice: When you grate your zucchini, if you notice a large amount of liquid pooling around it within a couple of minutes, you can blot it lightly with a paper towel. If it looks glistening with a little bit of moisture, but not soupy to the eye, just use it as-is.
Pro-Tips For The Best Cake
Use fabric baking strips on your cake pans. This cake is tall and having, even flat layer will help it be stable. Use water soaked baking strips on the outside of your pans, or learn how to make your own in my post about how to bake flat cake layers.
Weigh your ingredients. This is a crucial part in getting just the right cake texture. Weighing the flour prevents the cake from having too much and turning out dry. Weighing the grated zucchini eliminates the risk of adding more than you need and making the cake gummy from too much moisture.
If you’re nervous about decorating a layer cake, check out my post on how to decorate a cake! I give you all of the tips you need for making even frosting thickness between layers, doing a crumb coat, and additional decorative options like a ganache drip or piping.
How To Make Chocolate Zucchini Cake
Below are step-by-step images highlighting portions of the process to make this chocolate zucchini cake. You can find the full set of instructions and measurements in the recipe card below.
1. Whisk the dry and wet ingredients. In a large bowl, whisk together the flour, cocoa powder, baking soda, baking powder, espresso powder (if using), and salt. Sifting helps if your cocoa has lumps, but if it doesn’t, whisking is enough. Set the dry bowl aside. In another large bowl, whisk together the vegetable oil, granulated sugar, brown sugar, eggs, sour cream, and vanilla until smooth. The mixture should look glossy and homogeneous—no streaks of unincorporated brown sugar or egg whites.
2. Fold in the zucchini. Switch to a spatula and fold the grated zucchini into the wet mixture until it’s fully distributed. The mixture will look loose and chunky at this stage and may appear to get runnier—that’s normal, as the zucchini starts to release moisture.
3. Combine wet and dry. Pour the zucchini mixture into the bowl of dry ingredients. Stir with a spatula until almost combined (there should still be a few dry streaks visible). Add the chocolate chips and stir until they are well dispersed and no dry pockets remain. Stop the moment the batter looks uniform; over-mixing over develops gluten and toughens the crumb.
4. Divide and bake. Distribute the batter evenly among your three greased and lined cake pans. If you have fabric-soaked baking strips, wrap them around the outside of the pans. (Cake strips are not strictly required, but they make the difference between flat layers that stack cleanly and layers that need to be leveled). Bake at 350°F for 35 to 40 minutes, or until the centers are springy to the touch and the cakes have started to pull away from the sides of the pans. The top of the cakes may look glossier than a typical cake when they’re done—that’s the moisture from the zucchini. Let the layers cool in their pans for 10 minutes, then invert onto a wire rack. Peel off the parchment rounds once the layers are cool to the touch.
5. Make the ganache and buttercream. Combine chocolate chips with some of the heavy cream in a microwave-safe bowl. Microwave in 30-second intervals, stirring between each, until the chocolate is fully melted and smooth. Set aside to cool slightly (if it’s hot, it will melt the butter in the next step). In a stand mixer fitted with the paddle attachment, cream the room-temperature butter with the salt on medium speed until pale and fluffy. Sift in the cocoa powder and mix on low until combined. Scrape down the bowl. With the mixer on low, add the powdered sugar a little at a time, alternating with small pours of the remaining heavy cream. Once everything’s incorporated, add the vanilla and the cooled ganache. Increase the mixer to medium speed and beat until the frosting is light, fluffy, and easy to spread.
6. Assemble the cake. Transfer a cup of frosting to a piping bag fitted with an Ateco 869 open star tip—that’s the classic dollop tip—for finishing the cake’s top edge. Place a cooled cake layer on a stand or serving plate. Top with a cup of buttercream, spreading it edge-to-edge in an even layer. Repeat with the second layer. Place the third layer top-side-down so the cake’s top is flat (the bottom of the cake is the most level surface you have to work with).
7. Spread the remaining buttercream over the top and sides with an offset spatula, leaving a thicker layer on the top of the cake, and a thinner layer on the sides. If desired, you can mostly scrape the frosting off the sides for a naked cake-style frosting.
8. Pipe and chill. Pipe dollops of buttercream around the top edge of the cake using the reserved frosting. For clean slices, chill the assembled cake for at least 30 minutes before cutting. This firms up the buttercream so the knife passes cleanly through the cake instead of dragging and tearing it.
Chocolate Zucchini Cake
Equipment
- Stand mixer
- Three 8 inch cake pans
Ingredients
For the Cake:
- 3 cups all-purpose flour (360g)
- 1 cup unsweetened natural cocoa powder (100g)
- 1 tablespoon baking soda
- ¾ teaspoon baking powder
- 1 ½ teaspoons espresso powder optional
- ¾ teaspoon salt
- 1 ½ cups vegetable oil (354ml)
- 1 ½ cups granulated sugar (300g)
- 1 cup light brown sugar packed (220g)
- 6 large eggs room temperature
- ½ cup sour cream room temperature (120g)
- 1 tablespoon vanilla extract
- 4 ½ cups grated zucchini (about 3 medium zucchini) (475g)
- 1 ½ cups semi sweet chocolate chips (270g)
For the Buttercream:
- 1 cup semi sweet chocolate chips (180g)
- ⅔ cup heavy cream divided, (160ml)
- 5 ½ cups powdered sugar (660g)
- 1 ½ cups unsalted butter room temperature (282g)
- ½ teaspoon salt
- ⅓ cup unsweetened natural cocoa powder (33g)
- 1 ½ teaspoons vanilla extract
Instructions
For the Cake:
- Preheat the oven to 350ºF and grease three 8-inch cake pans with baking spray or butter and flour. Line the bottom with a parchment round, and wrap them with fabric soaked baking strips, if you have them.
- In a large bowl whisk together the flour, cocoa powder, baking soda, baking powder, espresso powder, and salt. Set aside.
- In another large bowl combine the vegetable oil, granulated sugar, brown sugar, eggs, sour cream and vanilla and whisk until smooth. With a spatula, fold the zucchini into the wet ingredients until fully incorporated.
- Pour the wet ingredients into the dry and stir until almost combined (there should be a few dry streaks remaining). Add in the chocolate chips and stir in until no dry streaks remain and the chocolate is well dispersed throughout the batter.
- Divide the batter evenly among the cake pans (about 3⅓ cups/810g each). Bake for 35 to 40 minutes or until the centers are springy to the touch and the cakes start to pull away from the sides of the pans. Allow the cakes to cool in the pan for 10 minutes before inverting onto a wire rack to cool completely. Remove the parchment paper once cooled.
For the Buttercream:
- Place the chocolate chips and ⅓ cup of the heavy cream in a small microwave safe bowl or a liquid measuring cup. Microwave in 30 second intervals, stirring between each, until the chocolate is fully melted. Set aside to cool while you make the frosting.
- In the bowl of a stand mixer fitted with a paddle attachment, cream the butter and salt on medium speed until light and creamy, about 3 minutes. Sift in the cocoa powder and mix on low until combined. Scrape down the bowl.
- While mixing on low, gradually add the powdered sugar, about 1 cup at a time, alternating with a small pour of the remaining ⅓ cup of heavy cream. Once all of the powdered sugar and cream is incorporated, add in the vanilla extract and melted cooled chocolate.
- Increase the mixer to medium speed and beat for 2 minutes or until the buttercream is very light, fluffy, and easy to spread. Transfer 1 cup (236g) of the frosting to a piping bag fitted with an open star tip (Ateco 869.)
For the Assembly:
- Place a cooled cake layer on a cake stand or serving plate and top with 1 cup of buttercream, spreading into an even layer all the way to the edge. Top with another cake layer and repeat with the buttercream. Top with the remaining cake layer, placing it top side down so the top of the cake is even. Spread the remaining buttercream all over the top and sides of the cake. I prefer to leave a thicker layer on top, and spread a thinner layer on the sides, then use an offset or bench scraper to remove most of the frosting on the sides. This gives the cake a naked cake look and a perfect balance of frosting to cake.
- Finish decorating the cake by piping dollops of buttercream around the top edge of the cake. For clean slices, chill the cake for at least 30 minutes before slicing so the frosting firms up a bit and the cake is easier to slice.
Notes
- Chill the cake before slicing. This firms up the frosting enough to make the cake stable to cut cleanly. A quick 30 minute chill will do the trick!
- Making this for a party? Use my technique for cutting a round cake to get more servings out of the cake to feed a crowd.
Nutrition
Make-Ahead & Storage
Make-ahead: Both the cake layers and the buttercream can be made up to 2 days in advance. Wrap the cooled cake layers in plastic wrap and keep at room temperature; refrigerate the buttercream in an airtight container and let it come back to room temperature before whipping briefly to restore the texture.
Storage: Once assembled, the cake keeps for up to 5 days in the refrigerator. Cover with a cake dome or wrap exposed cut surfaces with plastic to prevent the crumb from drying out. Pull the cake from the fridge about 30 minutes before serving. The buttercream tastes considerably better at a slightly warmer temperature than fridge-cold, and the cake itself softens back to its proper tender texture.
Freezing: The unfrosted layers freeze beautifully. Wrap each layer in plastic wrap and then foil, and freeze for up to 3 months. Thaw in the wrapping at room temperature for several hours before unwrapping. The chocolate buttercream also freezes well, separately, in an airtight container.
Variations And Substitutions
Cupcakes: This batter makes a generous 40-42 cupcakes. If you’d like to make less, cut the recipe by half. Fill the liners with ¼ of batter and bake at 350°F for 18 to 22 minutes, or until the centers spring back when gently pressed.
9×13 sheet cake: The full batter recipe fits a 9×13 pan. Bake at 350°F for 45 to 50 minutes. This will make a very thick sheet cake, and it takes a while to bake since the batter is so moist. Check the center by poking it first. If it feels springy, then test it with a toothpick—it should come out with a few moist crumbs. (If you poke it with a toothpick too soon, it can collapse the center of the cake, so do the spring test first.)
9-inch round cake: Divide the batter between three greased and lined cake pans. Bake at 350°F for 30 to 35 minutes. The layers will be thinner than the original recipe, so the cake will bake faster.
Frosting alternatives: If you’d rather skip the chocolate buttercream, this cake also works beautifully with cream cheese frosting, mocha frosting, or a whipped chocolate ganache. You will need 5-6 cups of frosting to cover the cake and pipe simple decorations on top.
Yellow squash: Yes, you can substitute yellow squash for the zucchini one-for-one! The cake reads identically in flavor and texture.
Frequently Asked Questions
No. Zucchini’s flavor is mild to begin with, and the cocoa, chocolate chips, and brown sugar overwhelm it completely once baked. The skin breaks down to dark green flecks, making it virtually indistinguishable from bits of chocolate. What you’ll taste is a fudgy chocolate cake from the zucchini’s moisture and tenderness.
No. Peeling is unnecessary. The skin is thin, soft, and breaks down completely during baking. If you’re trying to keep the zucchini secret from a particularly visual eater, peeling will eliminate any possible green flecks, but otherwise leave the skin on for the small nutritional fiber bump, and to save yourself time.
Yes, with one extra step. Frozen zucchini releases significantly more water on thawing than fresh, so thaw the zucchini fully and gently squeeze out some of the excess liquid in a clean kitchen towel before measuring (you don’t need to squeeze it dry). You’re trying to bring the moisture content down to roughly what fresh zucchini would contribute. Use the squeezed weight to match the recipe’s 475g.
Two likely culprits. The cake was underbaked—chocolate cakes can look done on top while the center is still wet, so always test to feel for the springy texture before you remove them from the oven. Overmixing the cake batter—if you mix the batter too much, the gluten will overdevelop and turn the cake chewy or gummy. Gently fold the wet ingredients into the dry, and stir just enough to disperse the chocolate chips. I chose to stir the zucchini into the wet ingredients instead of adding it directly to the combined cake batter like some other recipes. This eliminates a mixing step with the flour, reducing the risk of overmixing the batter!
More Cake Recipes To Try
If you liked this one, try one of my other cake recipes:
- Carrot and Walnut Cake — uses the same vegetable-as-moisture principle in a spice cake.
- Ultimate Chocolate Cake — my ultimate chocolate cake without the zucchini.
- Chocolate Zucchini Bread — for more zucchini baking, this fudgy loaf is perfect to slice alongside your morning coffee.
- Zucchini Brownies — these brownies use the same moisture trick with added zucchini for super fudgy squares.
- Chocolate Sheet Cake — the perfect chocolate cake built for crowds.
If you’ve tried this chocolate zucchini cake recipe, then don’t forget to rate it and let me know how you got on in the comments below. I love hearing from you!
Laurel says
I’ve been on a personal challenge of a 12 day baking spree during the Covid19 virus and I have a list of neighbors who signed up to be my guinea pigs. Every night at 7pm I make my rounds to everyone in my complex. I drop off on hoods of cars, little tables left by the front doors or a knock at the door for the “Treat Box”. I was on day 9 when I had a sudden plumbing problem so the kitchen was out of commission for a couple days. So I had to make something special to make up for it. This was the recipe! I snapped a pic and sent it saying “I’m back in business”. In 2 minutes I had 6 responses. “Yes”, “I want mine”, “Your making me fat”, “So professional looking”, “You know where to put it” and “I’m looking out my door for you”. Thank you John. This was easy and came out Perfect! Just like your picture, except my drips. How do you get the ball on the bottom of yours? Today I felt like a success and nailed a cake and brought happy stomachs to my neighbors during this uncertain time. Again, Thanks!
John Kanell says
It;s all about the ganache temp. try testing it out on a vertical surface.
Michelle Hillman says
I made this cake yesterday and it was off the charts! The zucchini is undetectable and the chocolate chips add an element of surprise! It is decadent and moist. The buttercream is not too sweet. Your recipes and tutorials have inspired me to start baking and have now discovered a new passion! Thank you, John!!
Melinda says
Delicious cake! Everyone loved it and asked for the recipe. I did not peel the zucchini and it was not a problem. You couldn’t tell it was there. Would definitely make it again.
Nicole says
Hey John,
I’ve been fascinated by the recept for a long time. I finaaly decided to make it this morning. It smells wonderful, but it’s been in the oven for an hour now and it’s still not done.
I did tweak the recipe a tiny bit by using a bit less oil and swapping brown sugar dor more white sugar and a bit of honey.
jkanell says
Hi Nicole! How did it turn out? The cake doesn’t really look that done when it’s baked, very glossy. Hope it all turned out.
Nicole says
It turned out fine!
It was tasty and gobbled up before the end of midday at my grandmas. 🙂
It did really need those extra minutes… or half hour. Maybe it’s just that I’m not used to that fudgy cakes but with extra time it was wonderful. As I said. I did a lot less oil. And I’m going to try it swapped with butter and with even less next time because I could taste the oil in the cake and it was very oily to touch. I don’t know why because I followed the rest of the measurements, but it still turned out delicious so I don’t regret anything haha!
Liz M says
I made this cake for a group last night and it was a huge success!! Everyone loved how moist and fudge-y it was, but it wasn’t too rich. My daughter said it’s the best chocolate cake she’s ever had. And, I didn’t peel the zucchini, but you still couldn’t find it. The chocolate buttercream was super easy to make, and we could even pipe it- the consistency was great. I also never did ganache in the microwave before, and it also turned out amazing. I did swap out the oil in the cake with butter, personal preference, and it was great!!!
jkanell says
SO happy you liked it!!!