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Rich, creamy Potatoes au Gratin is the ultimate potato recipe. Thinly sliced potatoes and onions bake in a rich cheese sauce until tender, golden, and bubbly. It comes together quickly with just a few simple ingredients, and it can be assembled or par-baked ahead of time for an easy make-ahead holiday side dish!
Potatoes au gratin is the perfect side dish to complete your holiday table. After years of testing these cheesy potatoes for my own family holiday dinners, I’ve discovered the best potatoes to use for potato gratin and the ideal thickness for slicing the potatoes. The right thickness of sliced potatoes, once baked in a rich, incredibly creamy cheese sauce, turns out perfectly tender yet still firm enough not to fall apart when you scoop it! I share all this and more in this updated post, so your au gratin potatoes are a hit every time!
“I LOVE this recipe. I used some chipotle garlic cheddar, gruyere, with some Vermont sharp cheddar. Added really banging heat and flavor!”
Sam
What Is The Difference Between Potatoes Au Gratin And Scalloped Potatoes?
While the terms “potatoes au gratin” and “scalloped potatoes” are often used interchangeably, there is a key difference between the two potato casserole recipes. Both terms refer to a dish of thinly sliced potatoes baked in a sauce. The type of sauce is where the difference comes in.
Scalloped potatoes are baked in a plain cream sauce (bechamel) with aromatics and herbs. Potatoes au gratin— also called Gratin Dauphinois— have cheese added to the sauce, making it a mornay sauce (a béchamel with cheese added!). Au gratin potatoes are sometimes topped with cheese or buttery breadcrumbs, while scalloped potatoes typically don’t have a topping.
Key Ingredients (+ Why I Use Starchy Potatoes)
These are the main ingredients you need to make homemade potatoes au gratin. You can find the full list of ingredients and measurements in the recipe card below.
Potatoes — starchier potatoes are the best choice for potato gratin. My go-to is russet potatoes. An all-purpose potato, like Yukon gold potatoes, also works, but use russets if you can, as they have more starch to help bind the gratin. You want a starchy potato, as the high level of natural starches from the potato helps the sauce coat and stick to the potatoes. This gives you a thicker, creamier casserole that holds together when scooped. Waxy potatoes (like red potatoes and baby potatoes) often bake up more slippery, causing the gratin to fall apart when scooped.
Onion — thinly sliced white onion shingled with the potatoes adds flavor and texture to the creamy au gratin potatoes. Feel free to swap for a yellow onion or shallots if that’s what you prefer or have on hand.
Roux — to make the roux, you’ll need unsalted butter and all-purpose flour. A roux helps to thicken the white sauce before you add the cheese. It also helps the cheese incorporate smoothly into the milk so that you end up with a creamy sauce instead of a greasy or clumpy one.
Milk — warm milk is key for a sauce without lumps, as it’s easier to incorporate with the warm roux ingredients. The drastic temperature difference of cold milk will cause the hot roux to seize and clump together.
Cheese — shredded Gruyere cheese and cheddar cheese add lots of flavor and decadence to the sauce. Shred the cheese yourself instead of buying pre-shredded cheese, which is sold with anti-clumping agents that prevent it from melting properly.
For Tender Potatoes, Slice To The Right Thickness
To start, use the right tool. A sharp chef’s knife will cut the potatoes easily for clean, even slices. I like to cut a thin sliver off one of the long sides of the potato to give myself a flat surface so the potato remains steady when I slice it. A quicker cutting option would be to use a mandoline for exactly even slices, but please be careful when using it and wear a cut glove or use the mandoline guard.
In my testing, I discovered cutting the potatoes into ⅛-inch-thick slices was the perfect thickness for tender but not mushy potatoes. This size means they’re thin enough to cook completely and become tender in the oven, while still being able to hold their shape and not fall apart when scooped. If they’re too thick (¼-inch or thicker), the potato slices won’t soften, so they’ll need to be baked longer. A longer bake time risks burning or drying out the cheese sauce. If you cut the potatoes too thin (1⁄16-inch), they will become mushy and overly soft by the time the cheese sauce browns on top.
Can I Make This Ahead Of Time?
Yes! You have two options for making cheesy au gratin potatoes ahead of time:
Assemble it ahead: You’ll slice the potatoes and onions and shingle them in your casserole dish, pour the cheese sauce over the potatoes and onions, then tightly cover with aluminum foil. Pop the assembled potato casserole into the refrigerator for up to 24 hours. When you are ready to bake, let it sit out at room temperature for 20 to 30 minutes before baking. (This eliminates the risk of your cold casserole cracking when it hits the hot oven.)
Par-bake it: Assemble the potatoes au gratin as directed in the recipe and bake for 1 hour. Allow it to cool to room temperature, then refrigerate it until you’re ready to finish baking it. The next day, let it sit out for 20 to 30 minutes. Then, bake for 20 minutes, covered, to rewarm the potatoes. Remove the foil and bake for another 20 to 30 minutes for the top to brown nicely. If it looks a bit dry when you remove the foil (which can sometimes happen as the potatoes absorb the sauce while it chills), just drizzle ⅓ cup more milk or heavy cream on top before you finish baking.
Using either of these make-ahead methods could potentially break the sauce when it’s baked, but you likely won’t notice since it’s so cheesy! And anyway, the time saved is worth it, especially if you’re prepping ahead for a big holiday meal!
FAQs And Troubleshooting Your Gratin
Yes! The easiest way to make gluten-free potatoes au gratin is to simply swap the all-purpose flour in the roux for your favorite gluten-free flour blend. The other ingredients are naturally gluten-free.
You can also make a flour-free version (without a roux) by swapping the whole milk for heavy cream. Heat the cream in a medium saucepan, and once it starts to bubble, remove it from the heat. Add in the cheese, salt, and black pepper, and stir until the cheese has melted. Continue with the recipe as written. Since heavy cream is thicker and fattier than milk, the fats in the cream and cheese will blind together better, eliminating the need for a roux.
If the potatoes look dry after the first hour of baking, simply add ⅓ to ½ cup milk or heavy cream to the baking dish before continuing to bake.
The most common issue when making au gratin potatoes is not cooking the potatoes long enough, so they don’t soften properly. Be sure to test the potatoes for tenderness with a fork or knife before removing them from the oven. Cutting the potatoes into too-thick slices is another reason they do not soften in the cooking time, so slice them no thicker than ⅛-inch thick.
If the potatoes are still very hard after the first hour, continue baking them covered, checking them every 10 to 15 minutes. You should feel some slight resistance when you insert a knife or fork into the center, but they shouldn’t feel hard. If they still aren’t tender at the end of baking, drizzle ¼ to ⅓ cup of milk on top, cover, and continue baking, checking every 10 to 15 minutes until tender.
Pro Tips For Making The Best Potato Gratin
Don’t lay the slices flat. Shingle them so they stack at an angle. Laying the slices in this way ensures the sauce seeps between the layers better, so you make the most of the rich flavors in the sauce.
Use a glass or ceramic baking dish to help prevent the sauce from burning on the edges. Glass and ceramic insulate heat better than metal. A metal pan can cause the edges to harden and brown too much.
Cover the pan tightly with foil for the first stage of baking. This traps steam and moisture in the baking dish to help the potatoes cook through and become tender without drying them out.
How To Make Potatoes Au Gratin
Below, I’ve highlighted portions of the recipe in step-by-step process images along with instructions for making the best potatoes au gratin. You can find the full set of instructions in the recipe card below.
1. Clean and peel the russet potatoes or Yukon golds and use a chef’s knife to thinly slice them. Then slice the onion. See my post on how to cut an onion for tips!
2. Arrange the sliced potatoes and onions in a shingled stack in a 2- to 3-quart casserole dish. Season the layers with salt and pepper as you go. Set aside while you work on the sauce.
3. Melt the butter in a medium pot, then add the flour and whisk constantly for 2 minutes to make a roux.
4. While whisking, slowly pour in the warm milk. Keep whisking until the mixture starts to bubble and thicken.
5. Remove the cream mixture from the heat and add the shredded cheese, salt, and pepper. Stir until the cheese has melted fully.
6. Pour the cheese sauce over the prepared potatoes and cover the pan with aluminum foil. Bake at 350°F for 1 hour, or until the potatoes resist slightly when a fork or knife is inserted into the center. Then, remove the foil and continue baking for 20 to 30 minutes so the top can turn nicely golden brown and the sauce can thicken up more. When they are done, a fork should easily insert into the potatoes at the center. Let the potatoes au gratin cool for 10 to 15 minutes to allow the sauce to set before serving.
Potatoes au Gratin Recipe
Ingredients
- 4 Russet potatoes (about 3 pounds/1.35kg)
- 1 medium white onion (275g)
- ¾ teaspoon salt plus more for seasoning
- ½ teaspoon pepper plus more for seasoning
- ¼ cup unsalted butter (56g)
- 3 tablespoons all-purpose flour
- 2 cups warm milk (480ml)
- ½ cup shredded Gruyere (60g)
- 1 cup shredded cheddar cheese (120g)
Instructions
- Preheat the oven to 350°F.
- Peel the potatoes, then thinly slice them about ⅛-inch thick. Peel, halve, and thinly slice the onion. Shingle the potato and onion slices in layers in a 2-quart to 3-quart casserole dish, seasoning the layers lightly with salt and pepper as you go. ( I used about ½ teaspoon of each when assembling the gratin.)
- In a medium pot, melt the butter over medium heat. Whisk in the flour. Cook whisking constantly, for 2 minutes. Drizzle in the warm milk while whisking. Continue whisking until the mixture starts to bubble and thicken slightly, 2 to 3 minutes.
- Remove from heat and stir in the shredded cheeses, salt, and pepper until the cheese is melted. Pour the cheese sauce over the potatoes. Cover the pan tightly with foil.
- Bake for 1 hour or until a fork can be inserted into the potatoes with slight resistance. (They should feel a little bit firm but not hard. If so, continue baking, checking every 10 to 15 minutes.)
- Carefully remove the foil and continue baking for an additional 20 to 30 minutes, or until the top is golden brown and the potatoes are tender. (You should be able to easily insert a fork into the center.) Let the gratin cool for 10 to 15 minutes, so the sauce thickens up slightly, before serving.
Notes
- You can assemble this dish ahead of time. Cover the casserole dish and refrigerate for up to 24 hours. Let it sit at room temperature for 30 minutes to 1 hour to take off some of the chill, and then bake it, covered, as directed.
- Store leftovers covered in the fridge for up to 4 days.
Nutrition
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Variations
You can add flavorings, use different cheeses, and even add a topping to change up this classic potatoes au gratin recipe. Here are some ideas:
- Add fresh herbs: Add 2 teaspoons of fresh herbs like thyme, oregano, chives, or rosemary to the creamy cheese sauce.
- Add garlic: Add 3 to 4 minced garlic cloves to the melted butter and cook until fragrant before adding the flour.
- Use a different onion: For a slightly sweeter onion flavor, use red onion instead of white onion.
- Add sweet potatoes: Use a mixture of sweet potatoes and russet potatoes for a more colorful side dish that also has lovely natural sweetness from the sweet potatoes.
- Cheese options: Use an aged or smoked cheese like Gouda or fontina in the sauce to change up the flavor. Or feel free to use any melty cheese you like, such as Colby and Monterey Jack. You could also add a little Parmesan cheese for nuttiness.
- Add a topping: Sprinkle extra shredded cheese over the top of the casserole once you remove the foil for the last bit of baking. You’ll get a bubbly, golden brown, extra gooey topping this way. You can also make a buttery bread crumb mixture by mixing 1 cup of store-bought Panko or homemade bread crumbs with 2 tablespoons of melted butter. Sprinkle it over the top of the potatoes after the first hour of baking.
What To Serve With Au Gratin Potatoes
Serve this au gratin potatoes recipe on your holiday table alongside roasted turkey, steak au poivre, glazed ham, roast beef, or turkey meatloaf.
It’s also a great complement to a variety of other holiday side dishes like glazed carrots, steamed broccoli or air fryer broccoli, green bean casserole, roasted butternut squash, cranberry sauce, or any of your favorite salads.
How should I store and reheat leftovers?
Storing: Once completely cooled to room temperature, tightly cover leftovers in the pan with plastic wrap or store them in an airtight container and refrigerate for up to 4 days.
Freezing: To freeze, transfer cooled potatoes au gratin to a freezer-safe container and freeze for up to 3 months. Thaw overnight in the refrigerator before reheating.
Reheating: Transfer the gratin potatoes to an oven-safe dish and reheat in a 350°F oven for about 15 minutes. For smaller portions, you can microwave it in 30-second intervals, stirring in between, to help prevent the sauce from breaking.
More Side Dish Recipes To Try
Try these potato recipes next if you need more side dish ideas!
Twice-baked potatoes have a cheesy filling with bacon bits and green onions. They work as a side dish for a special occasion, or a finger food for game day, or a party.
Hasselback potatoes are as delicious as they are visually impressive. They are so crispy, fluffy, and buttery!
You can never go wrong with simple roasted potatoes. They go with pretty much anything and work well for a regular weeknight dinner or as part of a big holiday spread.
Speaking of versatile, creamy, buttery mashed potatoes are simple, delicious, and pair well with various entrees. You can even make them ahead of time, so holiday meal prep is less overwhelming!
My easy sweet potato casserole is the perfect cross between a rich side dish and a decadent dessert. Make a tasty mashed sweet potato mixture and cover it with a crumbly pecan streusel topping before baking.
If you’ve tried this au gratin potatoes 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!
