01 - Set the oven to 320°F.
02 - Combine minced garlic, chopped rosemary, sea salt, black pepper, olive oil, lemon zest, and lemon juice in a small bowl to create a paste.
03 - Pat the lamb shoulder dry and evenly rub the marinade all over its surface.
04 - Place sliced onions, carrots, and celery in a large roasting pan as a bed for the lamb.
05 - Set the lamb shoulder atop the vegetables. Pour white wine and stock around the lamb without drenching it.
06 - Cover the roasting pan tightly with foil or its lid and place it in the oven for 3 hours.
07 - Remove the cover, increase the oven temperature to 400°F, and roast for another 30 minutes to develop a golden crust.
08 - Allow the lamb to rest for 15 minutes before carving. Serve alongside the roasted vegetables and pan juices.