Preheat the oven to 180C. Place the boneless lamb in a roasting dish.
(For best results use a dial meat thermometer with the point in the centre of the joint and the dial facing out of the oven)
Roast for 20 minutes per 500g. You are aiming for an internal temperature of 55C.
Remove from oven, place on a carving board and allow to rest at room temperature for 20 minutes. The temperature will rise whilst resting and the joint should be blushing pink when you carve.