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.

Nutrition per serving