Take a little gravy, a few cockles, oysters or mushrooms, put to them a little of the gravy that comes from the fish, either broiled or boiled, it will do very well if you have no other gravy, a little catchup and a lump of butter; if you have neither oysters nor cockles you may put in an anchovy or two, and thicken with flour; you may put in a few shred capers, or a little mango, if you have it.