Creamy Au Gratin Potatoes
3 tbs. butter3 tbs. flour1/2 tsp. salt2 c. milk1 1/2 c. shredded Cheddar cheese4 potatoes, sliced into 1/4-inch slices1 onion, sliced into ringsPreheat oven to 400F. Grease a 1-quart casserole dish.In a medium saucepan, melt butter over medium heat. Mix in the flour and salt and stir constantly with a whisk for one minute. Gradually add milk, whisking constantly, and continue cooking and stirring until thickened. Add cheese and cook and stir until melted.In the casserole dish, layer 1/3 of the potato slices, 1/2 of the onion slices, and 1/3 of the cheese sauce. Repeat layers, ending with potatoes and cheese sauce.Cover with aluminum foil and bake in the preheated oven for 1 1/2 hours.