Clean, sour, salt the fish. Do not thaw frozen fish.
Make a roux from margarine, milk and flour, season with mustard and the spices. Stir in the chopped parsley.
Put the fish in a greased baking dish and sprinkle with a little paprika powder. Pour the mustard sauce over it and bake in the oven for about 30 minutes.
This goes well with mashed potatoes and a green salad.