Add butter and mix well with pastry cutter (or by hand) until crumbly.
Put in a glass jar, cover tightly and store in refrigerator.
Makes 7 cups.
To make sauce: Combine mix (1/3 cup for thin, 1/2 cup for medium, 1 cup for thick) with 1 cup milk in a small deep heavy saucepan. Cook over medium heat, stirring frequently, for about 2 minutes. Remove from heat and use as desired.