01 - Set the oven to 320°F (160°C).
02 - Pat the lamb shoulder dry with paper towels. Using a sharp knife, make deep incisions all over the meat and insert peeled garlic cloves into the slits.
03 - Combine olive oil, rosemary, thyme, sea salt, and black pepper in a bowl. Rub this mixture thoroughly over the lamb shoulder.
04 - Place the sliced onions, carrot chunks, and celery pieces evenly in a large roasting pan. Position the lamb shoulder on top of the vegetables.
05 - Pour the white wine and stock around the lamb in the pan, avoiding pouring directly over the meat. Cover tightly with aluminum foil or a roasting lid.
06 - Roast in the oven for 3½ hours, occasionally basting the lamb with pan juices to maintain moisture.
07 - Increase oven temperature to 430°F (220°C). Remove the cover and continue roasting uncovered for 20 to 30 minutes until the lamb is golden and tender.
08 - Allow the meat to rest loosely covered with foil for 15 minutes before slicing or shredding. Serve alongside roasted vegetables and pan juices.