Have the fish cleaned by the fishmonger; rub it well with a handful of salt, to remove the slime peculiar to this fish, wash it well, and wipe it with a clean, dry cloth; stuff it with the following forcemeat.
Put the stale bread to soak in sufficient luke-warm water to cover it; meantime fry the chopped onion in the butter until it is light brown; then wring the bread dry in a clean towel, put it into the onion with the parsley, salt pork, capers or pickles, salt, white pepper, and broth or hot water; stir until it is scalding hot, when it will cleave from the bottom and sides of the sauce-pan; then stuff the fish with it.
Lay the fish in a dripping pan on the carrot, onion, bay leaf and parsley; cover the fish with slices of salt pork, season it with a saltspoonful of salt, and the pepper, and bake it in a moderate oven for half an hour, basting it occasionally with a little butter, or stock. When it is done, put it on a dish to keep hot while you prepare a sauce.
Strain the drippings in the pan, and add to them the walnut catsup, Worcestershire sauce, chopped capers, and chopped parsley. Pour a little of this sauce in the bottom of the dish under the fish, and serve the rest with it in a bowl.