01 - Preheat oven to 320°F.
02 - Pat lamb shoulder dry and rub evenly with olive oil, salt, and pepper.
03 - Make small incisions all over the lamb and insert halved garlic cloves into each slit.
04 - Place sliced onions in a large roasting pan and set lamb on top. Scatter rosemary, thyme, and bay leaves around.
05 - Pour white wine and stock around the lamb without pouring over it.
06 - Cover the pan tightly with foil or lid and roast in oven for 2 hours.
07 - After 2 hours, nestle carrots, parsnips, and potatoes around the lamb, then cover and continue roasting for another 2 hours.
08 - Remove cover, increase oven temperature to 400°F, and roast uncovered for 30 minutes to brown the lamb.
09 - Transfer lamb to a platter and let rest for 15 minutes.
10 - Skim excess fat from pan juices, serve lamb with vegetables and pan sauce.