In a heavy saucepan, melt the butter. Blend in the flour, salt and pepper. Add the milk all at once. Cook and stir over medium heat, continue cooking until mixture is thickened and bubbly. Cook and stir 2 minutes more. Makes 1 cup. Thin white sauce is pourable and is used for soups and creamed vegetables. Medium white sauce is thicker and is used for sauces, scalloped dishes and creamed dishes. Thick white sauce is used for croquettes and souffle's. For cheese sauce, add 1 cup shredded Sharp American cheese, stirring to melt.