Creamy au Gratin Potatoes

Ingredients

• 4 medium russet potatoes , thinly sliced
• 1 medium onion , sliced into rings
• salt and ground black pepper to taste
• 3 tablespoons butter
• 3 tablespoons all-purpose flour
• 0.5 teaspoons salt
• 2 cups milk
• 1.5 cups shredded Cheddar cheese

Instructions

1. 1

   Gather all ingredients. Preheat the oven to 400 degrees F (200 degrees C). Grease a 2-quart casserole dish with butter.

2. 2

   Layer 1/2 of the potatoes in the bottom of the prepared casserole dish; season with salt and pepper.

3. 3

   Layer onion slices over top, then top with with remaining potatoes. Season again with salt and pepper.

4. 4

   Melt butter in a medium saucepan over medium heat. Whisk in flour and salt; cook, whisking constantly, until raw flour flavor has cooked off, about 1 minute.

5. 5

   Gradually add milk, about 1/4 cup at a time, whisking well after each addition to incorporate; the gradual addition and whisking of milk will help avoid lumps in your sauce.

6. 6

   Cook, whisking constantly, until the mixture has thickened, 3 to 5 minutes.

7. 7

   Stir in cheese all at once; cook, stirring constantly, until melted, 30 to 60 seconds.

8. 8

   Pour cheese sauce over the potatoes, and cover the dish with aluminum foil.

9. 9

   Bake in the preheated oven until potatoes are tender and sauce is bubbly, about 1 ½ hours.