Preheat the oven to 170 Degrees Celsius . Rub the meat with olive oil and using a sharp knife, make small incisions in the lamb and place pieces of garlic and rosemary sprigs into the incisions. Season with salt and black pepper

Arrange the onions in a roasting tray and place the meat on top. Pour in the beef stock and wine and cover the tray with foil.

Roast in the preheated oven for 3 hours 30 minutes until tender

While the meat roasts, prepare the potatoes by rubbing a large roasting/casserole dish with butter.

Arrange the thinly sliced potatoes in the dish. Combine the dessert and cooking cream with the mustard powder and pour over the potatoes. Brush the tops of the potatoes generously with butter. Season to taste

Roast in the oven alongside the lamb for about 1 hour 30 minutes until the tops of the potatoes are golden brown and the potatoes are tender.

Once the lamb is tender, remove the foil from the dish and turn the oven up to 200 Degrees Celsius. Roast for a further 30 minutes until browned