Step 1

Preheat the oven to 200°C.

Step 2

Place the lamb on a work surface and rub all over with the salt and pepper.

Step 3

Pierce the lamb in a few places and insert the garlic halves.

Step 4

Heat the olive oil in a roasting pan over medium heat, add the sage and rosemary and cook briefly. Add the butter and allow to foam. Place the lamb on top and roast for 30 minutes. Reduce the heat to 150°C and roast for a further 2 hours.

Step 5

Transfer the lamb to a warm platter and leave to rest in a warm place for 30 minutes.

Step 6

Meanwhile, place the roasting pan on top of the stove over medium heat. Add the vinegar and stir to deglaze the pan juices. Add the wine and stock and simmer for 10 minutes. Strain into a clean pot and season. Add the mushrooms and cook for 2 minutes, then add the potatoes and lemon juice.

Step 7

Serve the lamb with the potatoes and mushrooms, drizzled with the pan juices.