Cut the mushrooms, if they are too large; throw them for a few minutes
into boiling water, then into cold water to whiten them; wipe well, and
_sauté_ them in a saucepan, with a little butter. When colored, and
almost done, sprinkle in a little flour and a little chopped parsley;
when the flour is cooked (which will require but a few moments), pour
in, say, a tea-cupful of stock; let it all simmer for about fifteen
minutes. Just before serving, stir in the beaten yolk of an egg, and a
few drops of lemon-juice. The sauce should be rather thick. Fill each
shell with this mixture; sprinkle a few sifted cracker-crumbs on the
tops; brown them slightly with a red-hot shovel, or put them into a very
hot oven a few moments just before serving.