Here is a basic recipe for making white sauce.
Thin--1 Tbs Butter, 1 Tbs Flour, 1 cup Milk, 1/4 tsp Salt--Use in soups and creamed vegetables.
Medium--2 Tbs Butter, 2 Tbs Flour, 1 cup Milk, 1/4 tsp Salt--Use in sauces, scalloped or creamed dishes.
Thick--3 Tbs Butter, 4 Tbs Flour, 1 cup Milk, 1/4 tsp Salt--Use in croquettes, souffles, fondu, or gravy.
Over low heat, melt butter in heavy saucepan. Blend in flour until smooth. Add milk all at once. Cook until thickened and bubbly, stirring constantly. Add salt. Remove from heat. Use in recipe. Yield: 1 cup.
You can substitute margarine or oil for the butter.
I also like to season my sauce with onions and garlic in the butter/oil, and I add chicken bouillon cubes with the milk for extra flavor. To hide the onions in the sauce, blend it up with a blender.
I used white sauce in my Cheesy Vegetable Soup, Baked Potato Soup, Fondu, and Baked Spaghetti.