Dissolve two ounces of butter in a stewpan, mix in the yolks of two eggs
lightly beaten, the juice of a lemon, and a pinch of pepper and salt,
stir this over the fire until thickened. Have ready half-a-pint of plain
butter sauce, and mix all gradually together, with a small tin of
champignons, or about the same quantity of fresh mushrooms chopped and
stewed gently for ten minutes in a little broth or milk. Stir them with
the liquor in which they have stewed into the sauce, and let them stand
for a few minutes, then spread the mixture on to neat slices of toasted
bread. The sauce must be a good thickness, so that it will not run off
the toast, and care must be taken in the first process not to oil the
butter or make the sauce lumpy.