Fresh herbs are essential for this stuffing but they can vary with the time of year.
Clean the fish, open up and remove the backbone and check that any other stray bones are discarded. Season the fish with salt and pepper and sprinkle with lemon juice. Set aside while you make the stuffing.
Cook the spinach in boiling salted water just until it collapses. Drain well, chop finely and press well in a sieve or colander to remove as much moisture as possible.
Return the spinach to the pan with half the olive oil and stir over moderate heat until the spinach has absorbed the oil. Stir in the chopped herbs, add a sprinkling of salt and remove from the heat.
Divide the herb stuffing between the fish and fold each fish back into shape. Place the mackerel, sprinkled with the remainder of the oil, in a lightly oiled baking dish or wrap in oiled foil for cooking on a barbecue.
Bake in a moderate oven (Mark 4, 180°C, 350°F) for 20–30 minutes until cooked. Serve hot or cold.
© 1987 Geraldene Holt. All rights reserved.