Easy Potatoes au Gratin

Ingredients

Steps

1. 1

   Preheat the oven to 350°F.

2. 2

   Peel the potatoes, then thinly slice them about 1/8-inch thick. Peel, halve, and thinly slice the onion.

3. 3

   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 (about 1/2 teaspoon of each total).

4. 4

   In a medium pot, melt the butter over medium heat. Whisk in the flour and cook, whisking constantly, for 2 minutes.

5. 5

   Drizzle in the warm milk while whisking. Continue whisking until the mixture starts to bubble and thicken slightly, 2 to 3 minutes.

6. 6

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

7. 7

   Pour the cheese sauce over the potatoes and cover the pan tightly with foil.

8. 8

   Bake for 1 hour, or until a fork can be inserted into the potatoes with slight resistance. They should feel a little firm but not hard; if not, continue baking and check every 10 to 15 minutes.

9. 9

   Carefully remove the foil and bake for an additional 20 to 30 minutes, until the top is golden brown and a fork slides easily into the center.

10. 10

    Let the gratin cool for 10 to 15 minutes so the sauce thickens slightly before serving.