Clean the fish well, and slice and pour over it one good cup of boiling vinegar. Make a Roux by putting one tablespoonful of lard into the stewpan, and when hot, add gradually two tablespoonfuls of flour, rubbed smoothly. When quite brown, take the Fish, which has been previously rubbed with salt and pepper, and place in the pot. Let it simmer gently a few minutes, and then add a large, chopped onion, parsley, one chopped clove of garlic, one sprig of thyme, a bay leaf, two blades of mace and eight or ten allspice. Let these brown and cover with water sufficient to prevent burning. Put the Fish on a slow fire to stew, and when half done, add a little Cayenne and, if possible, add two cups of White Port Wine. When done, place the Fish in a dish, pour the gravy over it, and garnish with Croutons, slices of lemon and serve with prepared horseradish.