Season the lamb with salt and pepper. Grease a roasting tin (pan) with the
oil and add the meat. Roast in a preheated oven at 220°C/425°F/gas mark 7
for 20 minutes, then reduce the temperature to 190°C/375°F/gas mark 5 and
continue to roast for 1.25 hours until crisp on the outside and cooked to
your liking. For different-sized joints, calculate the cooking time as 20
minutes per 450 g/1 lb plus 10 minutes.