1

Preheat the oven to 120°C, fan 100°C, gas mark ½. Rub the oil all over the lamb and set a large, heavy-based frying pan over a medium-high heat. Cook the joint for 5 minutes, turning, until browned all over. Transfer the lamb to a chopping board and leave to cool slightly. Using a sharp knife, cut deep slits into the meat, then stud with the anchovies and garlic.

2

Arrange the onion wedges in the base of a large roasting tin or ovenproof dish. Place the lamb on top of the onions and scatter over the rosemary sprigs. Pour 125ml water into the tin, then cover tightly with kitchen foil and bake for 4 hours.

3

Meanwhile, put the potatoes on a small baking tray and mist with cooking spray. Transfer the potatoes to the oven and bake alongside the lamb for the final 2 hours of cooking time.

4

Remove the lamb from the oven and keep it covered loosely with kitchen foil. Increase the oven temperature to 200°C, fan 180°C, gas mark 6 and cook the potatoes for a further 30 minutes, or until golden brown.

5

Serve the lamb and onion with the potatoes and steamed veg on the side, the extra rosemary sprigs scattered over the top and any juices from the pan spooned over the meat.