Cook the soaked beans in unsalted water for 1 1/2 hours or until tender. Allow the lamb to come up to room temperature.

Heat the oven to 170°C (325°F) gas 3. Butter a shallow, flameproof casserole or gratin dish just large enough to hold the leg of lamb comfortably.

Prick the lamb all over with the point of a sharp knife and insert a sliver of garlic in each incision. Season generously with salt and freshly ground black pepper. Place the lamb in the greased baking dish on a rack and sprinkle with the melted butter. Roast for 45 minutes.

Saute the coarsely chopped onion in 30 ml (2 tbsp) olive oil until transparent.

Remove the lamb from the rack. Spoon the drained cooked beans, chopped tomatoes, sauteed onions, finely chopped parsley and 60 ml (4 tbsp) olive oil into the dish in which the lamb was cooked. Place the lamb on top and cook for a further 25 minutes. Give the bean mixture a stir, then continue roasting for another 20 minutes, or until the lamb is tender and the juices run pink when the meat is pierced.

When the lamb is cooked, place it on a heated serving dish and leave to rest for 10 - 15 minutes in the turned-off oven, with the door open. Keep the bean mixture hot and when the lamb has rested add the bean mixture to the dish. Garnish with sprigs of flat-leaved parsley and serve.