Spanish Mackerel a la Viennet

Chop up separately some onions, shallots, and mushrooms; fry the onions and shallots in butter then add the chopped mushrooms; lay on top mackerel fillets pared half heart-shaped, season with salt, mignonette, and nutmeg; place over a liberal piece of butter, cover with a strong buttered paper, and set the pan in the oven for fifteen minutes, then drain off the butter, and add a little white wine, espagnole sauce (No. 414), and tomato sauce (No. 549). Dress the fish, reduce the sauce, and when ready pass through a tammy and pour it over the fillets.