Cut two onions into very small dice, and put them into a stewpan, with two ounces of butter; fry them a short time, but not to discolor them; have ready three or four handsful of well-washed sorrel, which cut into ribands and put into the stewpan with the onions, add one tablespoon of flour, then mix well a pint of milk and a quart of water; boil altogether twenty minutes, keeping it stirred; season with a teaspoonful of sugar and salt, take it from the fire, and stir in quickly a liaison* of two yolks of eggs mixed with a gill of cream or milk (it must not boil afterwards), put the crust of a French roll, cut into strips, in the tureen, pour the soup over, and serve very hot.