Serves 4
2 medium-sized mackerel
1 medium-sized onion
2-3 thin lemon slices
few black peppercorns
2 bay leaves
about 1/4 pint (150ml) wine vinegar about 1/4 pint (150ml) water
crisp lettuce, for serving
Mustard dressing
1 teaspoon French mustard
1 tablespoon wine vinegar
pinch of sugar (optional)
3 tablespoons water
salt and freshly milled black pepper 4 tablespoons oil
Clean the mackerel and remove the heads. Place in an ovenproof dish. Cut the tail fins off, if necessary, so the fish fit into the dish. Peel and thinly slice the onion. Arrange on top of the fish along with the lemon slices, peppercorns and bay leaves. Mix together the vinegar and water and pour it over the fish to cover. Add more vinegar and water in equal parts to cover the fish, if necessary. Cover the dish with kitchen foil and cook in an oven heated to 350°F (180°C) or Gas no. 4 for 45 minutes. Allow mackerel to cool in the liquid, preferably overnight.
Combine the mustard, vinegar, sugar, if using it, water and a seasoning of salt and pepper in a bowl. Beat in the oil until the dressing is well blended.
Transfer the fish to a work surface and carefully remove the skin, then lift the fish from the bones. Arrange the crisp lettuce on a serving plate and place the fish on top. Hand the dressing separately. Serve with thinly sliced brown bread and butter.