In a medium bowl, combine the dry milk powder, flour, salt, and white pepper (if using) and mix well with a whisk.
With a pastry blender or two knives, cut in the butter or margarine until mixture resembles cornmeal and no large pieces of butter remain.
To make white sauce using the mix, combine ½ cup mix and 1 cup cool water in a small saucepan.
Cook over low heat until smooth, stirring constantly with a whisk. Season as desired. Makes about 1 cup sauce.
