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This easy key lime pie sets up in just 10 minutes with a four-ingredient filling—and it’s not magic, it’s science! With twice the filling of most recipes, my crust trick makes sure it all fits for a slice that is generous and sturdy.
Most key lime pie recipes make a shallow pie using one can of condensed milk for a modest layer of filling. This one is not that way! I like a generous slice of pie, so during my recipe testing I doubled the filling and found that it comes almost to the top of the pie dish now. But not every pie dish is the same depth, so with my trick, you can shape the crust in a way that ensures it holds all of the filling in. (See my Pro Tips below!)
I also tested this recipe with a non-dairy alternative to prove the science behind why this filling sets up so nicely, even with a short 10-minute bake. I discovered the key is in the reaction between milk proteins and acid, and you can see it starting to happen in the mixing bowl!
“I tried key lime pie for the first time in Florida this winter. When I returned home I went directly to Preppy Kitchen to see how John makes his. I have now made this 4 times and everyone raves about it. I have used both Biscoff (my favorite) and graham cracker crumbs. Both are delicious.”
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Key Ingredients
These are the main ingredients you need to make this easy key lime pie. You can find the full list of ingredients and measurements in the recipe card below.
Sweetened condensed milk — not only does condensed milk add sweetness, but it also makes the filling luscious, velvety, and so creamy. Be sure to use a dairy version. The milk proteins are essential to setting the pie filling.
Key limes — you need key lime juice and lime zest to add tang and brightness. Key limes are small, very flavorful, and slightly sweeter than regular limes. They were synonymous with the Florida Keys, where they used to grow in abundance. This pie can be made with regular limes if you don’t have key limes.
Egg yolks — egg yolks add richness and help the filling set. Separate the yolks from the whites when the eggs are cold. The yolk and whites will be firmer, reducing the risk of them breaking.
Crust — to make the crisp graham cracker crumb crust, you only need graham cracker crumbs, melted butter, and sugar.
Key Limes Versus Regular Limes
You can tell the difference immediately from their size. Key limes are smaller, about 1 inch in diameter, and more aromatic. Regular Persian limes (what you mainly find in grocery stores) are two to three times larger, and milder in flavor but more sour.
Be realistic about the labor: it takes roughly seven regular limes to get three-quarters of a cup of juice, and about 24 key limes for the same amount. Regular limes are much easier to juice with a reamer than key limes are. A hand-held press juicer or a garlic press works well on key limes when you have a lot to squeeze.
Bottled key lime juice is a genuinely fine option here, which is not something I say often. The condensed milk is sweet and rich enough to cover most of the flavor difference between fresh and bottled juice. Nellie & Joe’s Key West Lime Juice is the one I prefer. I’ve used the bottled juice in my key lime cake and key lime pie bars, too, so it’s a great swap in all kinds of desserts.
Pro Tips For The Best Key Lime Pie
Mound the crust slightly at the edge of the pie dish. This is a very full pie, and if you press the crust level with the top of the pan, the filling may spill out in a spot or two before it sets. If your pie dish is 1½ inches deep or less, make sure the crust comes up about ½ inch above the rim. If the dish is closer to 2 inches deep, you won’t need to worry much about it!
Packaged crumbs need more butter than freshly ground. Store-bought graham crumbs are drier, so expect to use the full 8 tablespoons. If you grind 12 to 14 full sheets yourself, 6 tablespoons is usually enough. Do the pinch test: take a pinch of the mixture between your thumb and two fingers, or a small scoop in your fist, squeeze, and let go. If it holds its shape, it is ready to press. If it collapses into sand, stir in another tablespoon of butter and test again. My graham cracker crust recipe has more details!
Choosing the Right Pan: Deep Or Shallow
I tested this recipe for a standard 9-inch plate, about 1½ to 1¾ inches deep.
In a deep-dish pan (2+ inches deep), press the crust to the top edge rather than mounding it, and be careful not to spread the crumbs too thin. A thin crust falls apart when sliced.
9” store-bought crumb crusts are shallower than a homemade crust, so expect leftover filling. Divide it between two shells, use a 10” pie crust, or bake the extra filling as a few mini pies or in ramekins.
Why The Bake Time Is So Short
Ten minutes seems impossibly short for a custard, but it works thanks to science!
The acid in the lime juice reacts with the proteins in the egg yolks and the condensed milk and causes them to bond and thicken on their own, without heat. You can actually feel this starting to happen in the mixing bowl. At first, the mixture will feel runny, but as you whisk until everything is smooth and combined, you will feel it getting thicker within a few seconds. Technically, the pie would set without baking once it’s chilled.
The short bake does two things: it firms the set beyond what the acid alone achieves, and it applies some heat to the raw eggs for safe consumption. It is not there to cook the filling through in the way a pumpkin pie needs cooking through, but it’s an added layer of structure and safety.
You will know it is done when the surface shows a few tiny holes from air bubbles popping, or the center wobbles very slightly when you shake the dish. Then it needs at least an hour in the fridge. Cooling the filling down makes it thicker so it slices more cleanly.
How To Make Key Lime Pie
Below, I’ve highlighted portions of the recipe in step-by-step process images along with instructions for making homemade key lime pie. You can find the full set of instructions in the recipe card below.
1. Make the crust: Stir the graham cracker crumbs, sugar, and 6 tablespoons of melted butter together. Do the pinch test to see if it needs more butter: squeeze a small amount in your hand, add more butter a tablespoon at a time until it holds together if needed.
2. Press the crumbs into a 9-inch pie plate, making it smooth across the base and up the sides, and mounding the rim slightly above the edge of the dish. Pinch the rim to compact it. Bake for 10 minutes, until dry and slightly darker around the edge.
3. Make the filling: Whisk the sweetened condensed milk, lime juice, egg yolks, and zest together in a bowl until smooth. Wait to mix the filling until the crust is out of the oven, or it won’t settle into as smooth a top in the crust (it thickens as it sits).
4. Fill and 10-minute bake: Pour the filling into the warm crust and jiggle the dish lightly to level it. Bake for 10 minutes, until the surface is smooth and the center wobbles slightly. Cool the pie on a rack for about 20 minutes, then chill for at least an hour.
5. Top the pie: Whip the cream with the powdered sugar and vanilla to soft peaks.
6. Dollop or pipe the whipped cream over the pie and finish with zest.
Can I Make This Dairy Free?
I get asked this question all the time, but the answer is no without modification. We just covered the science of the reaction between the milk proteins and the acidic lime juice to set the filling. Sweetened condensed coconut milk doesn’t have the same proteins, so they don’t form the same bond or strong structure, and the pie filling actually melts in the oven.
I tested this to show you and you can see the results in the image below. I made one key lime pie as written, and then made another, only replacing the dairy condensed milk with coconut condensed milk. You can see the coconut version formed a foamy top, and then when sliced, the custard had turned to soup. Even when I first mixed the filling before baking, the mixture stayed runny instead of turning thick.
After that test, I modified how the filling was combined and tested a cooked custard method. This heated the eggs so the egg proteins coagulated and bonded with the milk fats and sugar, and set the custard. Success!
For a non-dairy key lime pie: Swap the dairy milk 1-for-1 with sweetened condensed coconut milk. Mix the same filling ingredients together with the coconut milk, then add them to a medium saucepan. Cook over medium heat, stirring constantly, until the mixture thickens and reaches 170°F, 8-10 minutes. Immediately pour it into the baked pie shell and let it cool on the counter before chilling.
Key Lime Pie Recipe
Equipment
- 9-inch pie plate
- Mixing Bowls
Ingredients
For the Crust
- 1½ cups graham cracker crumbs (180g)
- 6 to 8 tablespoons unsalted butter (87g to 113g), melted, divided
- ¼ cup granulated sugar (50g)
For the Filling
- 2 (14-ounce, 396g) cans sweetened condensed milk
- ¾ cup key lime juice (180mL)
- 4 egg yolks
- 2 teaspoons lime or key lime zest
For the Topping
- 1 cup heavy cream (240mL)
- 3 tablespoons powdered sugar
- 1 teaspoon vanilla extract
- Optional: Lime zest and thinly sliced key limes
Instructions
For the Crust:
- Preheat the oven to 350°F.
- In a medium bowl, stir together graham cracker crumbs, 6 tablespoons of melted butter, and sugar until well moistened. Pinch the crumbs between your thumb, pointer and middle fingers. If they feel moist and stick together when released from the pinch, they are ready to be pressed in the pan. If they feel dry, sandy, and lose their shape when released from the pinch, stir in more butter, 1 tablespoon at a time.
- Add the crumb mixture to the pie plate. Using the flat bottom of a measuring cup or glass, firmly press the mixture into the bottom of the pan and up the sides of the pan, mounding the edge slightly above the rim of the pie plate. (Your hands or a flat spatula may be helpful to press the sides of the crust.) Bake the crust for 10 minutes, until dry and golden brown.
For the Filling:
- In a large bowl, combine the sweetened condensed milk, key lime juice, egg yolks, and zest. Whisk to combine.
- Pour the filling into the warm crust and give it a jiggle to level things out. Bake at 350°F for about 10 minutes. Cool on a wire rack for about 20 minutes, then chill for at least an hour. You’ll see some tiny holes in the pie and it will jiggle slightly when it’s done baking.
- Place a large mixing bowl or the bowl of a stand mixer along with the beaters or whisk attachment in the fridge or freezer until well chilled, at least 20 minutes.
For the Topping:
- In a large, chilled bowl, combine the cream, sugar, and vanilla. With a handheld mixer (or in a stand mixer with a whisk attachment), beat on medium speed until frothy and starting to thicken, about 2 minutes. Increase the speed to medium-high and beat until soft to medium peaks form, 1 to 2 more minutes.
- Top the pie with dollops of whipped cream, lime zest, and slices if you like, and serve.
Notes
- Biscoff crust variation. Process one 8.8-ounce package of Biscoff cookies to crumbs, reduce the butter to ¼ cup, and omit the sugar.
Nutrition
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Storing It
Cover and refrigerate the pie for up to 4 days.
It freezes well for up to 3 months, with or without the whipped cream. The texture of the filling changes slightly when thawing, turning a bit curdled or weeping, so serve it while still partly frozen. It’s actually very good that way, closer to a frozen custard! My Pie Academy includes details for how to freeze a pie (whole or slices) and avoid freezer burn.
Frequently Asked Questions
They keep about four days in the fridge and freeze well for several months. Four whites is exactly the amount you need for a pavlova or a batch of meringue cookies. You can also use them to make an egg white omelet for a savory option.
Yes, and it is better for it! The filling needs chilling anyway, so bake the pie the night before, refrigerate it uncovered until cold, and then cover it. Whip the cream and top it on the day you serve.
It’s not chilled long enough, or you used the wrong ingredient. Give it a full hour minimum and preferably longer in the fridge. If you cut into it warm, the filling will look loose even when you made it right. If you accidentally purchased a non-dairy milk, the filling won’t ever set up correctly, so check your can labels.
More Pie Recipes To Try
Try one of these pie recipes for another chilled pie option:
- Lemon Meringue Pie — another diner classic, the lemon curd filling is topped with toasted cloud-like meringue.
- Coconut Cream Pie — a tropical custard filling packed with toasted coconut; this can be made with a non-dairy alternative!
- Banana Cream Pie — a vanilla custard set with sliced bananas throughout.
- Millionaire Pie — the same graham crust with a creamy filling that doesn’t need to go in the oven at all.
- Chocolate Pie — no-bake chocolate pudding fills a buttery blind baked crust.
If you’ve tried this key lime pie 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!
