Wash and clean the mullet, salt them and let them sit for 20 minutes. Treat them with oil, slit their bellies and fill them with parsley and lemon juice. Wrap each mullet in baking paper and place in a tray to toast for 1/2 hour.
Remove the paper and put the fish in a dish. Fry 2 tablespoons of flour in butter in a dish on the stove and add the black pepper. Add the peeled and finely pre-chopped tomatoes. Salt to taste and once you get a sauce, thin it out with milk. Allow the sauce to boil for another 3-4 minutes and remove from the heat.
Optionally, add lemon juice and chopped parsley. Alternatively, you can prepare the sauce and put it together with the baked fish in a tray and let brown for 10-odd minutes.