01 - Position oven rack in the center. Preheat oven to 320°F.
02 - In a medium mixing bowl, whisk together harissa paste, olive oil, minced garlic, ground cumin, ground coriander, smoked paprika, lemon zest, lemon juice, sea salt, and black pepper until a thick paste forms.
03 - Pat the lamb shoulder thoroughly dry with paper towels. Using clean hands or a pastry brush, rub the harissa marinade generously over all surfaces of the lamb, pressing into crevices to ensure complete coverage.
04 - Scatter the sliced red onions, carrot chunks, and halved garlic bulb evenly across the bottom of a large roasting pan to create a vegetable bed.
05 - Place the marinated lamb shoulder directly on top of the vegetable bed, fat-side facing up.
06 - Pour the chicken or lamb stock and white wine around the base of the lamb, taking care not to wash off the marinade from the meat surface.
07 - Cover the roasting pan tightly with aluminum foil, sealing edges to trap steam. Transfer to oven and roast for 3½ hours.
08 - Remove foil and increase oven temperature to 390°F. Return lamb to oven and roast uncovered for 30 minutes, basting once with pan juices halfway through, until exterior is deeply caramelized and mahogany-colored.
09 - Remove from oven and tent loosely with foil. Let lamb rest for 15 minutes to allow juices to redistribute throughout the meat.
10 - Transfer lamb to a cutting board. Shred meat with forks or carve into slices. Serve with roasted vegetables and spoon pan juices over portions.