Creamy Au Gratin Potatoes
1. Heat oven 400 degrees. Grease a 9x13 inch casserole dish.
2. Layer half of the potatoes on the bottom of the dish. Top with all of the onion slices. Add the remaining half of the potatoes. Season with salt and pepper.
3. In a saucepan, melt butter over medium heat. Stir in flour and salt. Use a whisk and continue to stir for one minute. Whisk in milk. Cook until the mix has thickened. Stir in cheese all at once. Stir until cheese has melted (about 1 minute). Pour cheese mix over potatoes. Cover with foil and bake for 1 1/2 hours. During the last five minutes of baking, toss a sprinkling of cheese on top and continue baking until the cheese has melted.