Name: Potatoes Au Gratin
Prep time: 20 min
Cook time: 90 min
Total time: 125 min
Ingredients: 2½ pounds red potatoes; 1 medium onion (thinly sliced); 3 tablespoons butter; 3 tablespoons all-purpose flour; 1 teaspoon dry mustard powder; 2 cups milk; 1 cup shredded cheddar cheese; ½ cup shredded gruyere cheese; ¾ teaspoon salt (divided); ½ teaspoon black pepper (divided)

Potatoes au gratin is the perfect side dish for Sunday supper or as a make-ahead holiday side dish. Tender layers of potatoes and onions are baked in a rich, creamy, cheesy sauce until hot, bubbly, and golden.

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This recipe makes creamy potatoes, similar to scalloped potatoes but loaded with rich cheesy flavor. They are the perfect dish next to a baked ham, roast beef tenderloin or pork tenderloin.

Flavor: Creamy, cheesy, and comforting with a golden, slightly crispy top that makes every bite irresistible.
Why it works: A cooked roux thickens the sauce so it coats the potatoes instead of pooling thin at the bottom.
Recommended Tools: To save time on prep and make even and thin potato and onion slices, use a mandoline or the side of a box grater.
Time-Saving Tip: For the holidays, I usually put it together ahead of time and then bake it fresh just before serving. It makes life so much easier.

potatoes , cheese , milk , onion , flour , butter, mustard powder , salt and pepper with labels to make Potatoes Au Gratin

So what is the difference between scalloped potatoes and au gratin potatoes? They’re both very similar, containing potatoes (and often onions) baked in a creamy sauce. Au Gratin is defined as covered with breadcrumbs or cheese, scalloped refers to “bake with milk or a sauce”.

In the case of this recipe, the difference is the cheese. That being said, the term scalloped potatoes is still often used if there is cheese within the dish!

Best Potatoes to Use for Potatoes au Gratin

Red-skinned or Yukon Gold potatoes are best for gratin because they hold their shape and don’t need peeling, while starchy russets can turn mushy and are better for mashing.

Onions: Slice paper-thin so it softens fully and doesn’t stay crunchy.
Mustard Powder: A small amount enhances the cheese flavor (I also add it to my baked mac and cheese!). Swap in a little Dijon stirred off the heat.
Cheese: For the best potatoes au gratin, use bold, sharp cheeses like Gruyère or cheddar, with provolone or Swiss as good substitutes.
Variations: Add flavor with minced garlic, garlic powder, or fresh herbs like thyme or rosemary. You could also include ham or cooked bacon for a heartier casserole.

Sliced potatoes and onions for potatoes au gratin

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

Placing sliced potatoes and onions in a dish for potatoes au gratin

How to Make Potatoes Au Gratin

Prep: Thinly slice the potatoes and onions (full recipe below).
Assemble: Stack the potato slices and onions in the casserole dish.
Sauce: Cook the cheese sauce in a saucepan, then pour it over the potato and onion slices.
Bake: Bake until the potatoes are tender and the sauce is bubbly.

PRO TIP: For a quicker version, layer potatoes and onions, cover, and microwave 10 minutes. Add cheese sauce and bake 45–55 minutes as directed. Just as delicious, but a little quicker!

a skillet with butter making cheese sauce for au gratin potatoes

Adding milk to potatoes au gratin sauce in a skillet

Adding cheese to potatoes au gratin sauce in a skillet

A skillet of cheese sauce for potatoes au gratin

Use a mandoline to keep slices even so the casserole cooks at the same speed. Bonus, it makes prep way quicker.
Cook the flour and butter for a couple of minutes before adding milk to cook out the flour taste and for a thicker sauce.
Melt cheese off-heat so it stays silky and doesn’t turn grainy.
Spray the foil so it lifts cleanly without pulling cheese from the top.
If the top browns early, loosely tent with foil while the potatoes finish cooking.
Rest 15 minutes so the sauce sets and portions lift out neatly.

Make-Ahead, Storing, and Reheating

Make up to 24 hours ahead. Keep potatoes covered in sauce, cover tightly, and refrigerate. Bring to room temperature before baking, and add 10–20 minutes to the bake time.

Leftover potatoes au gratin will keep in the refrigerator for up to 4 days. Let it cool completely, then cover tightly with plastic wrap, or transfer to an airtight container before refrigerating.

To freeze, allow it to cool completely and wrap the dish well with both plastic wrap and aluminum foil, or portion it into freezer-safe containers. It will keep for up to 2 months in the freezer.

For best results, thaw overnight in the refrigerator before reheating. Reheat covered in the oven at 350°F until hot throughout (about 20 to 30 minutes), removing the cover near the end to crisp up the top again. Avoid microwaving frozen potatoes, as it can make the sauce grainy and the potatoes watery.

More Holiday Side Dishes

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image of Everyday Comfort cookbook by Holly Nilsson of Spend With Pennies plus text

Potatoes Au Gratin with a fork and a title

rich and cheesy Potatoes Au Gratin with writing

cheesy Potatoes Au Gratin in a dish with a fork and a title

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About the author

Holly Nilsson is the creator of Spend With Pennies, where she creates easy, comforting recipes made for real life. She is also the author of “Everyday Comfort,” which promises to inspire even more hearty, home-cooked meals.
See more posts by Holly