Preheat oven to 220°C. Place the lamb on a large sheet of tin foil and then in a roasting tin. Cut the garlic heads horizontally and put into the lamb parcel along with some rosemary, a good drizzle of olive oil and seasoning. Wrap up in the tin foil and cook for 30 minutes on a high heat, then turn down the oven to 170°C and cook for another 3½ to 4 hours. Allow to cool slightly and serve slices of lamb with your favourite potato dish.
Leftover lamb salad