01 - Set the oven temperature to 320°F.
02 - Dry the lamb shoulder with paper towels, then make small incisions all over the meat and insert garlic halves into each cut.
03 - Combine rosemary, thyme, oregano, lemon zest, sea salt, black pepper, and smoked paprika in a bowl. Rub the herb mixture evenly over the lamb, pressing it into the incisions.
04 - Heat olive oil in a large roasting pan over medium-high heat. Sear the lamb on all sides until it develops a golden-brown crust, about 5 to 7 minutes. Remove from heat and set aside.
05 - Distribute the sliced onions, carrots, and celery evenly on the bottom of the roasting pan. Position the lamb shoulder on top of the vegetables.
06 - Pour the white wine and stock around the lamb, avoiding pouring directly over the meat. Cover the pan tightly with a lid or heavy-duty foil.
07 - Place the roasting pan in the oven and cook for 3.5 to 4 hours, basting once or twice during cooking, until the lamb is exceptionally tender and pulls away easily from the bone.
08 - Remove the cover and continue roasting uncovered for an additional 30 minutes to develop a rich, browned exterior.
09 - Transfer the lamb to a serving platter and tent with foil. Let it rest for 15 minutes before carving. Serve with the roasted vegetables and pan juices.