Potatoes Au Gratin

Potatoes Au Gratin sounds fancy, but it’s easy to make and a delicious way to prepare potatoes!

In this gratin recipe, potatoes and onions are thinly sliced and baked in a rich cheesy sauce until bubbly and golden brown.

They’re perfect for Sunday supper or to serve with any holiday meal!

creamy Potatoes Au Gratin on a plate with a fork

Ingredients for Potatoes au Gratin

Potatoes: The best potatoes for potatoes au gratin are waxy potatoes like red-skinned or Yukon gold. They hold their shape well, and because they’re thin-skinned, they do not require peeling (extra bonus!).
- Note: While russet potatoes or baking potatoes will work and taste good in this recipe, they’re more starchy and may fall apart once cooked—they’re more suited to mashed potatoes.
Onion: Thinly sliced onion adds flavor to these potatoes. For a milder flavor, cook the onion in butter first or replace it with 1 teaspoon of onion powder in the sauce.
Cheese: I use cheese with a lot of bold flavors in this recipe, including cheddar, parmesan, and Gruyere.
- Option: Gruyère cheese adds a rich flavor to the cheese sauce but can be replaced with provolone or Swiss for a similar flavor!
Sauce: Butter and flour create a roux to thicken this sauce, and I use milk as the base. It’s plenty rich enough with all of the cheese.

a skillet with butter making cheese sauce for au gratin potatoes

Adding milk to potatoes au gratin sauce in a skillet

How to make Potatoes Au Gratin

Here is a quick overview of the steps for potatoes au gratin.

Prep: Thinly slice the potatoes and onions.
Sauce: Make the cheese sauce in a saucepan on the stove.
Assemble: Stack the potato slices and onions in little piles and then stand them on their sides in the casserole dish.
Bake: Bake until the potatoes are tender and the sauce is bubbly.

Find the full detailed recipe below.

Sliced potatoes and onions for potatoes au gratin

A small stack of sliced potatoes and onions for potatoes au gratin

Holly’s Pro Tips

For easy prep and even thin slices, use an inexpensive mandoline. You can find them for under $20, and it saves a lot of time.
Pre-shredded cheese will work in this recipe, however the sauce will be smoother if you shred cheese from a block.
If swapping the cheese, make sure you use those with bold flavors.
If you’re short on time, set the potatoes and onions in the dish as directed and cover with plastic wrap. Microwave on full power for about 10 minutes (it will be hot when removing the plastic wrap). Add the cheese sauce and bake as directed below for about 45-55 minutes. Just as delicious… but a little bit quicker!

How to Make Potatoes au Gratin Ahead of Time

This dish can be made 24 hours in advance. Ensure the potatoes are completely covered in the sauce—any exposed bits of potatoes will discolor slightly. Cover tightly with plastic wrap and refrigerate.

Remove from the fridge at least 30 minutes before baking. You may need to add 10 to 20 minutes to the baking time.

While we often eat these as a side, I sometimes make Potatoes au Gratin with ham by including slices or diced leftover ham (from our favorite crock pot ham) before baking.

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Tender potato and onion slices are layered and baked in a rich and delicious cheese sauce.

Prep Time 20 minutes

Cook Time 1 hour 30 minutes

Total Time 1 hour 50 minutes

Cook ModePrevent your screen from going dark

Preheat oven to 400°F.
Wash potatoes and slice into ⅛” thin slices. Slice onion as thin as possible.
Season the potatoes and onions with ½ teaspoon of salt and ¼ teaspoon of pepper. Toss well to evenly coat. Layer potatoes and onions into little stacks. Place stacks on their side in a greased 2.5qt to 3qt casserole dish.
Melt butter and flour in a saucepan and cook 2 to 3 minutes. Add mustard powder, ¼ teaspoon salt, ¼ teaspoon pepper and milk. Whisk over medium heat until thick and bubbly. Remove from heat and stir in cheeses until melted.
Pour the cheese sauce over the potatoes, gently separating them to allow the sauce to seep between the layers. Cover with foil (sprayed with cooking spray) and bake 60 minutes.
Remove foil and bake an additional 20 to 30 minutes or until lightly browned and potatoes are cooked. Cool 15 minutes before serving.

Slice potatoes as thinly as possible.
Shred your own cheese from a block for the best results. Fresh herbs (such as thyme or rosemary) and garlic can be added to the sauce if desired.
To reduce baking time, wrap casserole dish in plastic wrap before adding the cheese sauce and microwave on full power for about 10 minutes (be careful, it will be hot when removing the plastic wrap). Add the cheese sauce and bake as directed for about 45-55 minutes.
Additional cheese (cheddar or parmesan) can be sprinkled on top once the foil is removed if desired.
Store leftovers in an airtight container for up to 4 days. Reheat in the oven or the microwave.

Nutrition information provided is an estimate and will vary based on cooking methods and brands of ingredients used.

Course Side Dish

Cuisine American, French

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