This is a recipe in the Betty Crocker Cookbook which I found on line at cdkitchen
Serves 6Wash potatoes. Pare thinly. Cut into enough thin slices to measure about 4 cups.
Cook and stir onion in margarine in 2-quart saucepan until onion is tender. Stir in flour, salt and pepper. Cook over low heat, stirring constantly, until mixture is bubbly; remove from heat. Stir in milk and 1-1/2 cups of the cheese. Heat to boiling, stirring constantly. Boil and stir 1 minute.
Place potatoes in ungreased 1-1/2-quart casserole. Pour cheese sauce on potatoes. Cook uncovered in 325° F. oven 1 hour 20 minutes or in 375° F. oven 1 hour.
Mix remaining cheese and the bread crumbs; sprinkle over potatoes. Sprinkle
with paprika. Cook uncovered until top is brown and bubbly, 15 to 20 minutes
longer.