Preheat the oven to 200C. While the oven is warming, get a good handful of rosemary, mix with a good slosh of oil, a pinch of sea salt and cracked black pepper. Rub all over the mutton shoulder.
In a roasting dish add some halved onions and a pouch of stock. Place a roasting rack on top and place the shoulder onto the rack.
Roast for 30 minutes. It should begin to have a lovely brown colour.
Reduce the oven temperature to 130C, cover with foil and continue to roast for 4 hours. The meat will be completely tender and will fall off the bone.