Soften the onion and carrot in the olive oil. Stir in 2 cloves crushed garlic, 1 sprig chopped rosemary and the tomato. Season and add the sugar. Simmer for 5 to 10 minutes.

Add the beans and stir. Pour in the stock and wine, and simmer for 5 minutes. Add more stock if necessary. Check seasoning. Turn into a large, well-oiled roasting pan.

Prepare the lamb by cutting slits all over it with the point of a small, sharp knife. Insert slices of the remaining garlic and tiny sprigs of rosemary into the incisions. Moisten with olive oil and season. Place the lamb on top of the prepared beans and cover with 2 sheets of oiled baking paper.

Roast in a preheated oven at 160°C for 3 hours, until the lamb is very tender. If necessary, moisten the beans with a little more stock from time to time.