Remove the joint from the packaging, pat dry and bring to room temperature. Preheat your over to 180C for fan assisted or 200C for ovens without a fa (gas mark 6). Choose a large, heavy based roasting tray, ideally with deep sides and handles for easy movement. Place the joint skin side up then place in the centre of the oven and roast for 20 minutes per 500g reaching a core temperature of 72C. Remove from the oven, put onto a clean tray and keep warm by covering with a sheet of foil. Rest for a minimum of 20 minutes before carving.