Haul out a smallish roasting pan – we used one 32.5cm x 23.5cm. You want the lamb to fit quite snugly so the juice doesn’t evaporate too quickly. Lay onion, garlic and rosemary on the bottom of the pan. Rub lamb with olive oil and oregano and place on top of vegetables. Mix lemon juice and stock together and pour over lamb. Cover the whole roasting pan tightly with foil. Bake in a 120ºC oven for 8–10 hours until meltingly tender and falling off the bone.