Remove the lamb from the refrigerator about 2 hours before you intend to roast it. Meanwhile, make the stock. Put the bone in a saucepan with the carrot, bouquet garni, 500 ml (18 fl oz) water and a little salt and pepper. Bring to the boil, cover and simmer the stock for 30 minutes.

Strain the stock into a clean pan, add the onions, bring to the boil, cover and cook for 5 minutes. Remove the onions and reserve. Boil the stock until it is reduced to 300 ml ( 10 fl oz), then reserve.

Heat the oven to 190C (375F) gas 5. Put the port and redcurrant jelly in a small pan and add 30 ml (2 tbsp) stock. Whisk the mixture over a moderate heat until smooth.

Use the lard to grease a small roasting tin, then put in the joint with the join underneath. Surround it with the onions and put a small piece of butter on each onion. Brush the joint with the glaze. Put the tin in the oven and roast for 1 hour, brushing the joint generously with the glaze twice more during this time. The second time also brush the onions with glaze.

Transfer the joint and onions to a warm serving dish and leave to settle in a warm place while you make the gravy.

Stir the flour into the fat in the roasting tin, put it over moderate heat and cook for 1 minute, stirring. Gradually add the reserved stock and bring to the boil, scraping up any sediment and juices in the pan. Simmer for 3 minutes, then season to taste with salt and pepper. Strain into a warm sauce-boat.

Carve the meat, garnish with flat-leaved parsley and serve with the gravy.