How to Make It
Preheat the oven to 300°. Rub the lamb all over with the garlic and rosemary. In a small bowl, mix 2 tablespoons of the olive oil with the soy sauce and rub all over the lamb. Season the lamb with salt and pepper and shape the meat into a compact roll. Tie the lamb at 1-inch intervals with butcher’s twine. Set the lamb in a small roasting pan.
In a medium saucepan, boil the wine over high heat for 3 minutes. Add the beef stock and bring to a boil. Pour the stock over the lamb and braise it on the upper rack for about 3 1/2 hours, basting occasionally, until richly browned on top and tender.
Meanwhile, peel the shallots, leaving the roots and tops intact. In a small shallow baking dish, combine the shallots with the chicken stock and butter. Cover the dish with foil and bake the shallots next to the lamb for about 45 minutes, basting them a few times, until very tender. Remove the shallots from the oven.
Transfer the lamb to a carving board and cover loosely with foil. Pour the braising liquid back into the saucepan and skim off the fat. Boil the jus over high heat until reduced to 1 cup, about 5 minutes.
Increase the oven temperature to 400°. On a large rimmed baking sheet, toss the celery root with the remaining 3 tablespoons of olive oil and season with salt and pepper. Bake in the center of the oven for about 30 minutes, stirring halfway through, until browned and tender.
Meanwhile, baste the shallots. Bake them on the upper rack of the oven for about 25 minutes, basting occasionally, until glazed and browned. Add the glazed shallots and ginger to the lamb jus.
Untie the lamb. Carve the lamb crosswise into 1-inch-thick slices.
Arrange the lamb on plates and top with the shallots and jus. Garnish with the parsley and serve with the roasted celery root.