Simmer a spiced and seasoned Court Bouillon preferably with white wine for 1 hour.
Leave the heads on the mackerel, and clean the fish by drawing out the livers, etc., through the top of the body so the fish remains whole.
Chop up a handful of green or not very ripe gooseberries rather coarsely, adding 3 tablespoonfuls of butter or margarine and the mixed herbs, stuff the mackerel with them, and put the fish into the Court Bouillon.
Poach on a gentle heat for 25 minutes.
Boil the rest of the gooseberries peeled and with the pips removed in salted water, for 10 minutes.
Drain the fruit, and put it in the top of a double pan with 4 tablespoonfuls of butter, or margarine, salt, pepper arid grated nutmeg; fill the lower half of the double saucepan with hot water and let the sauce "melt" rather than cook.
Take the mackerel out of the stock, and cover with the gooseberry sauce.