FRENCH SAUCE
Rub together 1 tablespoon of flour and 1 of butter, and put in a saucepan; as it melts add slowly 1 cup of boiling water or vegetable stock, let boil, stirring constantly, then remove from the fire, and when somewhat cooled add the juice of 1 lemon, 2 tablespoons of tarragon or chervil vinegar, 2 egg-yolks slightly beaten, and salt and pepper.