Whitefish a la Gerhardi

Split a whitefish in two along the spinal bone; remove this, then season. Lay the fish on a buttered dish, moisten with white wine, add chopped up onions, then let cook to reduce the liquid to the consistency of a half-glaze; mix into it a Hollandaise sauce (No. 477). Dress the fish and surround it with blanched oysters, mushrooms and shrimp tails; pour two-thirds of the sauce over, and serve the remainder in a sauce-boat.