One ounce of butter put in a thick saucepan; when melted add one ounce of flour, stir them, let them bubble one minute; then pour in - stirring all the while - half a pint of hot broth or white stock, or if you have not it, hot water and the liquid from a can of mushooms. Let it boil, take from the fire, wait a minute and stir in gradually the yolks of three eggs, a saltspoon of salt, a quarter one of pepper; return it to the fire, stirring carefully; it must get to the boiling point, or the eggs will not be cooked, yet on no account boil, or it will curdle; when it is off the fire, stir in a tablespoonful more butter. If it should be too thick, add a very little broth or hot water.