1/4   pound butter cut into small pieces
   1/2   cup flour
    1    quart milk
   1/2   teaspoon salt
   1/4   teaspoon pepper

In blender put: milk, then flour, then butter.
Cover and blend at high speed 10 - 15 seconds until thoroughly mixed.
Pour into top of a double boiler and stir over simmering water until thickened.
Use a no stick saucepan if possible.