Preheat the oven to 150C/300F/Gas 2
For the lamb confit, heat the oil in a roasting tray. Place the lamb in the tray and cook, turning frequently, until lightly brown on all sides. Allow to cool slightly. Rub the lamb with the half head of garlic and a little sea salt. Add the white wine to the roasting tray along with the half head of garlic and four sprigs of rosemary.
Tightly wrap tin foil around the tray with the lamb in it, twice to ensure it is completely sealed. Place into the oven for approximately six hours (or overnight).
When cooked, the lamb should be very tender and easily removed from the bone using two forks. Remove all the meat from the bone and allow to cool. Cover and place in the fridge. Transfer any juices from the roasting tray into a jug and leave to one side.
For the torte, preheat the oven to 180C/350F/ Gas 4. Cover the bottom of a large baking dish with the olive oil and chopped garlic. Overlap about a quarter of the potatoes in the bottom of the dish until it is completely covered. Season with salt and freshly ground black pepper and sprinkle with a third of the chopped rosemary and parsley.
Lay half the lamb pieces over the potato to form a solid layer about 1.5cm/¾in thick. Repeat the process with another layer of herbs, potatoes and the remaining lamb.
Finally, arrange a double layer of potato on the top and again season with salt and freshly ground black pepper and the remaining herbs. Pour over the lamb juices and cover with tin foil. Place in the oven for about an hour and a half, or until the potatoes are cooked through.
To serve, slice the torte into ten and place the slices onto serving plates.