Spread the fat surface with a mixture of mustard and black pepper. Add some peeled shallots or onion halves around the joint to give extra flavour and colour to the gravy. Set oven to Gas Mark 6, 200°C (400°F). Place the joint in the hot oven for 15 minutes, reduce the temperature to Gas Mark 4, 180°C (350°C) and allow 15 minutes per 1/2 kg for rare, plus 20 minutes extra for medium or 30 minutes extra for well done. To be absolutely accurate, use a meat roasting thermometer. When the meat is cooked remove from the oven, cover loosely with foil and allow to rest for 30 minutes. This resting time allows the juices to settle; the meat firms up so it is easier to carve.
Spoon off the fat. Add some wine or water to the juices. Boil over a high heat and taste for seasoning. Serve with the sliced roast. Delicious with crispy roast potatoes, roast vegetables or a creamy vegetable purée.