Creamy au Gratin Potatoes

Ingredients

• medium russet potatoes, thinly slice d
• medium onion, slice d into rings
• salt and ground black pepper to taste
• tablespoon sbutter
• tablespoon sall-purpose flour
• 1/2 teaspoon salt
• cup smilk
• 1/2 cup sshredded Cheddar cheese

Instructions

1. Gather all ingredients. Preheat the oven to 400 degrees F (200 degrees C). Grease a 2 quart casserole dish with butter. Dotdash Meredith Food Studios
2. Layer 1/2 of the potatoes in the bottom of the prepared casserole dish; season with salt and pepper. Dotdash Meredith Food Studios
3. Layer onion slices over top, then top with with remaining potatoes. Season again with salt and pepper. Dotdash Meredith Food Studios
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. Dotdash Meredith Food Studios
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. Dotdash Meredith Food Studios
6. Cook, whisking constantly, until the mixture has thickened, 3 to 5 minutes. Dotdash Meredith Food Studios
7. Stir in cheese all at once; cook, stirring constantly, until melted, 30 to 60 seconds. Dotdash Meredith Food Studios
8. Pour cheese sauce over the potatoes, and cover the dish with aluminum foil. Dotdash Meredith Food Studios
9. Bake in the preheated oven until potatoes are tender and sauce is bubbly, about 1 ½ hours. Dotdash Meredith Food Studios