Press half a cup of peas and the liquid in which they were cooked through a sieve.   Melt a tablespoonful of butter; add a tablespoonful of flour and one-fourth a teaspoonful each of salt and black pepper and cook until frothy in the butter; add one cup of milk and cook, stirring constantly, until smooth and boiling; add the pea puree and stir until smoothly blended and again boiling.  If too thick add a little hot milk or broth with additional salt and pepper and serve at once.  If canned peas are used, add to them half a teaspoonful of sugar.