Remove the fillets from two chickens, separating them into large and mignon fillets; remove the membrane from the large fillets and the tendons from the mignon or small fillets and trim neatly. Cut transverse slits in the upper side of each fillet and, in the larger, insert slices of truffle stamped into rounds with the lower edge fringed, and tiny strips of truffle, in the smaller fillets. Smoked and cooked beef tongue may be used in the place of the truffles. Brush the fillets with beaten white of egg and dispose in a buttered agate baking-pan; turn in a few spoonfuls of rich broth or wine and cook about fifteen minutes covered closely with a buttered paper. Sprinkle the fillets with a little salt before brushing with the egg. Dispose around a socle of fried bread. Garnish the top with heart leaves of lettuce and surround the base with a velouté sauce to which the trimmings of the truffles, chopped fine, and eight medium-sized mushroom caps sautéd in butter have been added.