Cut a lattice pattern into the skin of the lamb. Cut the garlic into thin sticks and use to spike the lamb. Mix the tomato puree with the flour, salt, lemon juice, caraway and crushed peppercorns. Brush the mixture on to the lamb and leave it to marinate in a cool place for 12 hours.

Quarter the onions. Heat the oil in a roasting tin on the hob, seal the lamb and add the onions and half the stock. Roast the lamb on the bottom shelf of a very hot oven (240°C, 475°F, gas 9) for 15 minutes, then reduce the heat to moderately hot (200°C, 400°F, gas 6) and roast the meat for a further 40 minutes, basting frequently with the roasting juices and gradually adding the wine and the remaining stock.

At the end of the cooking time, turn off the oven, transfer the lamb to a plate and leave it to stand in the oven for about 10 minutes. Dilute the roasting juices with a little hot water and thicken with the cornflour dissolved in a little cold water.