How to Make It
Preheat the oven to 150°C/300°F/Gas Mark 2. Rub the lamb with 1 tablespoon of the olive oil and season well with salt and pepper. Place in a roasting dish with a lid and roast for 3 hours. Increase the temperature to 200°C/400°F/Gas Mark 6 and roast for another hour, or until the meat has begun to break apart. Turn the oven off and leave the meat in there to rest until needed, but in any event for at least 20 minutes.
While the meat is roasting, pod the beans (if using fresh ones) and cook in a pan of boiling water for 5 minutes. Refresh in cold water, then squeeze them out of their skins and set aside.
Now make the gravy. My method is unorthodox, but ensures less greasiness than the usual way. Heat the remaining olive oil in a clean pan, add the carrot, onion, celery and garlic and brown gently for 10 minutes. Stir in 1 teaspoon sugar and the tomato purée (paste) and let this brown too. Pour in all but 1 teaspoon of the vinegar and cook to reduce to a syrupy glaze. Tip in the wine, scrape up all the browned bits from the bottom of the pan and let bubble. Add the herb sprig and stock (broth), simmer for 10 minutes, then strain and set aside.
Once the meat is resting, melt the butter in a pan, add a pinch of sugar, the mint, a good pinch of salt and the remaining wine vinegar. Bubble for 1 minute, then tip in the skinned beans along with 2–3 tablespoons water and cook for another 2–3 minutes.
Reheat the gravy in a pan, spooning in some of the meat juices if desired, but be careful to skim off any excess fat.
To serve, carve the lamb into thick slices and serve with the beans, gravy and buttered new potatoes.