Christmas Leg of Lamb with Garlic Potato Gratin, Pancetta Beans & Red-Wine Gravy

Heat the oven to 190°C (170°C fan). Remove the lamb’s packaging and check its weight and the cooking instructions supplied. Pat the joint dry with kitchen paper. Mix 50g butter with the Rosemary, 1 tsp Garlic Granules, ¼ tsp Coarse Ground Pepper and a little salt. Rub over the lamb without cutting into the meat.

Place the lamb on a rack in a deep metal roasting tin, with the fattier side uppermost. Pour 150ml Lamb Stock into the tin beneath it. Roast uncovered, allowing approximately 2–2½ hours for the example 2.5kg joint, depending on its shape and your preferred doneness. Check the tin occasionally and add a splash of hot water if the juices are drying out. Cover the top loosely with foil only if it is browning too quickly.

While the lamb starts roasting, grease a deep ovenproof dish, approximately 30 × 25cm, with 10g butter. Warm the cream and milk in a saucepan with the remaining Garlic Granules, remaining ¼ tsp Coarse Ground Pepper and a little salt. Bring just to a gentle simmer, then remove from the heat.

Arrange the thinly sliced potatoes in overlapping layers in the greased dish. Pour over the warm cream mixture and press down gently so the liquid settles between the slices. Do not rinse the sliced potatoes, as their starch helps thicken the sauce. Cover the dish with foil and place on a baking tray on a shelf below the lamb, approximately 30 minutes after the lamb went into the oven.

Bake the gratin for 45 minutes, then remove the foil and bake for another 30–45 minutes, until golden and a small knife slides easily through the potatoes. If the top colours before the potatoes are tender, cover loosely again. If ready before the lamb, cover and keep warm; it can return to the oven briefly while the meat rests.

Start checking the lamb after approximately 1½ hours. Insert a clean food thermometer into the centre of the thickest part, avoiding the bone. For a medium finish, aim to remove the joint at approximately 60–62°C; the temperature will continue rising during resting. This lower temperature applies only to the specified intact, unrolled joint, with all outside surfaces thoroughly cooked. Rolled or stuffed joints must be cooked throughout, for example to 75°C for 30 seconds. Follow the supplied instructions and thermometer readings rather than the clock alone.

Transfer the cooked lamb to a warm platter or carving board, cover loosely with foil and rest for 25–30 minutes. Finish cooking the gratin if necessary, then let it stand for 10 minutes before serving so the creamy layers settle.

While the lamb rests, melt 20g butter in a saucepan over a medium-low heat. Add the shallots and cook for 8–10 minutes until softened and lightly golden. Stir in the Thyme, then add the red wine or additional stock. Simmer for 5–7 minutes until reduced by roughly half.

Spoon the excess fat from the lamb roasting tin, leaving the cooking juices. Add the remaining 150ml Lamb Stock and scrape up the browned juices with a wooden spoon. Pour through a sieve into the saucepan of shallots. Stir in the Lamb Gravy and simmer gently for 5–8 minutes until piping hot. Add any juices collected beneath the resting lamb, bring back to a simmer and taste before adjusting the seasoning.

Meanwhile, fry the Pancetta in a large frying pan over a medium heat for 6–8 minutes until golden and cooked through. Cook the green beans in boiling water for 4–6 minutes until tender, then drain thoroughly. Add to the pancetta with the remaining 20g butter and toss over the heat for 1–2 minutes. Taste before adding salt, as the pancetta already provides seasoning.

Carve the lamb into slices across the grain, working around the bone. Serve with generous spoonfuls of garlic potato gratin and the pancetta green beans. Bring the red-wine gravy to the table in a warmed gravy boat.