Melt the butter or lard in a deep frying pan and, when hot, add the onion, finely chopped, and fry till brown. Sprinkle with 1 tablespoon of flour, mix well and brown. Add the chopped tomatoes, the garlic and herbs, the allspice and a seasoning of salt and pepper. Mix well, and add the lemon juice, the claret and sufficient hot water to thin down the sauce—it should be somewhat thin at this stage. Simmer gently for about 10 minutes, mixing well. Then add the slices of fish and simmer till the fish is tender. The time varies with the quality of the fish and the thickness of the slices—turbot, in ½ inch steaks, takes about 20 to 25 minutes. The sauce should not be too thick; it should be of the consistency of thin cream. To serve, put the slices of fish on a hot dish, pour the sauce over them, and garnish with potatoes cut in cubes and fried a light golden colour in butter.