Squeeze the juice out of a lemon, remove the seeds, and chop the pulp fine with a bunch of parsley. Add a little of the grated peel. Cook together one tablespoonful each of butter and flour, add the parsley and lemon and one and one half cupfuls of stock. Season with salt, pepper, and powdered mace, and boil for ten minutes. Take from the fire, add the yolks of two eggs beaten with a little cold stock, and serve.