Lemon Cream Sauce

Put in a tin pail or cup 1½ cups milk, the yolks of 2 eggs and 2 tablespoonfuls
sugar; set in a vessel of hot water; beat with an egg beater until the sauce comes to a boil; remove from the fire; add ½ teaspoonful lemon essence; beat the whites to a stiff froth and stir them into the sauce.