3 tablespoons butter
3 tablespoons flour
1/2 cup chicken or vegetable broth
1/2 cup milk
salt and pepper to taste
Melt butter in pan, stir in flour and cook, stirring rapidly until thick. Slowly pour in broth while stirring, then stir in milk. Cook until thickened. Remove from heat and stir in salt and pepper.
This can be kept in the refrigerator for a couple of days.
You can vary this by adding mushrooms, sauteed celery, etc.