Cut an incision down the back of a mackerel, close to the bone, season it with a little pepper, salt, and cayenne, if approved of, butter the skin well, and place the fish upon a gridiron over a moderate fire, for about twenty minutes, turning it over when half done; when done, have ready two ounces of mai'tre d' hotel butter, half of which put in the incision at the back, previously putting the mackerel upon a hot dish without a napkin, spread the other half over; place it in the oven a few minutes, and serve very hot.