Place the fish in a greased casserole. Skin and chop the tomatoes, peel and finely chop the onion. Mix the tomatoes, onion, parsley (if used) and wine together, season and pour over the fish. Cover the casserole and cook in a fairly hot oven (400° F., Gas 6) for 30–35 min. Remove from the oven, lift the fish on to a hot dish and keep hot while making the sauce. Measure the tomato mixture and make up to ½ pt. with water if necessary. Melt the fat, add the flour and cook for 1–2 min. Add the tomato mixture, bring to the boil, stirring all the time and boil gently for 5 min. Season to taste, then pour over the fish and serve at once.