Roast leg of lamb

• 1 leg of lamb weighing 1.5-1.6 kg (3-3½ lb)
• 1 large onion

Trim away the excess fat at the top of the leg and remove the knuckle.

Heat the oven to 190°C, 375°F, Gas Mark 5. Put the sliced onion and thyme in the roasting tin and put the leg of lamb on top. Spread the butter over the lamb and then pour the oil over this. Put into the middle of the oven and roast, basting frequently for 1½–2 hours. Remove the lamb and put it on a dish, keep it hot