Potatoes au Gratin

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No holiday or celebratory meal is complete without a potato side dish. Regardless of the preparation, potatoes almost always cook up into the kind of savory and comforting dish that complements nearly any protein and delights family members and friends of all ages.

These cheesy potatoes are no exception! Made with sliced potatoes and onions, a rich and creamy cheese sauce, and baked until golden and bubbly, they’re a perfect side dish for Easter, Thanksgiving, Christmas, or Sunday dinners with the family. These cheesy potatoes are a no-fail recipe that is always sure to delight. For more classic potato recipes, try my twice-baked potatoes recipe, hasselback potatoes recipe, and easy roasted potatoes.

What You Need to Make This Recipe

An overhead shot of all the ingredients you need to make potatoes au gratin

Potatoes – the best potatoes to choose are russet or Yukon gold potatoes. Their mild flavor and starch level make russets an ideal choice for this recipe. Red potatoes can be substituted in a pinch, but the texture of the dish may be slightly different as red potatoes tend to get much softer and more crumbly than their creamier counterparts.

Onion – a white onion, peeled and sliced very thin. Alternatively, a yellow onion can substitute.

Unsalted Butter – opt for unsalted butter, as brands add differing salt levels to the salted varieties. If all you have is salted butter, reduce the added salt in the recipe by a pinch.

Cheese – in particular, sharp cheddar cheese and gruyere cheese. Purchase the cheese by the block and shred it with a cheese grater for the smoothest ultra-cheesy sauce. For an Italian-inspired twist on these cheesy potatoes, substitute shredded parmesan cheese for the cheddar.

Milk – choose whole milk if possible for the richest texture and flavor, though 2% milk can also work. Alternatively, for an ultra-luscious and creamy sauce, you can use a 1:1 mixture of whole milk and heavy cream or half and half.

How to Make Potatoes Au Gratin

Set of two photos showing potatoes sliced and then potatoes and onions slices layered into a baking dish

1. Preheat the oven to 350°F. Peel and thinly slice the potatoes, about ⅛-inch thick.

2. 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 each layer lightly with salt and pepper as you go.

Set of two photos showing flour added to melted butter and milk added.

3. In a medium pot or large saucepan, melt butter over medium heat. Whisk in the all-purpose flour. Cook, whisking constantly, for 2 minutes.

4. Drizzle in the warm milk while whisking. Continue whisking until the mixture starts to bubble and has thickened slightly.

Set of two photos showing cheese added to the pot to create a cheese sauce that's poured over the casserole dish.

5. Remove from heat and stir in the shredded cheeses, salt, and black pepper until the cheese is melted.

6. Pour the cheese sauce over the potatoes and spread out evenly. Cover the casserole dish with aluminum foil. Bake for 1 hour. Remove the foil and bake for an additional 20 to 30 minutes or until the top is golden brown and the potatoes are tender when pierced with a knife.

An overhead view of a plate of potatoes au gratin with a glass of wine beside it.

Pro Tips For Making This Recipe

Cut thin and even potato slices. This will help the potatoes to cook evenly and thoroughly. I recommend using a mandoline or sharp knife to create uniform ⅛-inch thick slices.
Use warm milk. For the best results, heat the milk on medium heat in the microwave or low heat on the stove until it is 100-110 degrees Fahrenheit before using it in the recipe. This will help the cheese sauce come together more easily and is less likely to clump the roux, resulting in a silky smooth sauce.
Bake the casserole for the full cooking time. The most common issue when making au gratin potatoes is not cooking the potatoes long enough; so be sure to cook them the full time and to test the potatoes for tenderness with a sharp knife before removing from the oven.
Remove the aluminum foil towards the end of baking. Or for the final 20-30 minutes. Cooking the potatoes covered allows the potatoes to steam and soften, but uncovering at the end will allow them to brown up nicely and for the cheese sauce to thicken up to be perfectly velvety.
Potato au gratin variations. Top with buttery bread crumbs, add fresh thyme or other herbs to the sauce, sprinkle the top of the potatoes with extra cheese or try using an aged or smoked cheese like Gouda or fontina in the sauce, swap red onion instead of white, or use a mixture of sweet potatoes and russet potatoes.

A plate of potatoes au gratin with a glass of wine in the background.

Frequently Asked Questions

How do I store leftovers?

Cool the potato casserole to room temperature and store leftovers covered in plastic wrap or in an airtight container in the refrigerator for up to 5 days. The potatoes can also be frozen in a freezer-safe container or zip-top bag for up to 3 months. Defrost in the refrigerator for 8-12 hours, or until partially thawed. Reheat in the microwave on medium heat for 1-2 minute intervals, or until heated through.

What do I serve with this?

Serve this au gratin potatoes recipe on your holiday table alongside roasted turkey, steak au poivre, glazed ham, or turkey meatloaf. It’s also a great compliment to almost any green vegetable or other side dishes, like glazed carrots, steamed broccoli, green bean casserole, or salad.

What is the difference between potatoes au gratin and scalloped potatoes?

Classically, the difference between scalloped potatoes and potatoes au gratin recipes comes down to the use of cheese and other ingredients used to make the sauce. Both are layered potato dishes, but the au gratin variety is topped with a rich cheese sauce, whereas scalloped are traditionally made with a cream and stock-based sauce.

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