method
1. Preheat oven to 350°F (180°C).
2. Place lamb in roasting tin, then rub the oil into the skin. Either make small slits in the meat and insert fresh rosemary leaves, or sprinkle surface with dried rosemary, then season well. Add water to the tin and cook for 3 - 3 1/2 hours - the meat should almost be falling off the bone.
3. Meanwhile, peel, parboil and dry the potatoes. Add them to the roasting tin 1 1/2 hours before end of cooking time and turn them till coated in fat. Turn again once during roasting.
