01 - Preheat the oven to 320 degrees Fahrenheit.
02 - Pat the lamb shoulder dry and rub all sides with olive oil, salt, and black pepper.
03 - Make small incisions all over the lamb using a sharp knife and insert halved garlic cloves into each cut.
04 - Place sliced onions evenly in a large roasting pan, set the lamb on top, and scatter rosemary, thyme, and bay leaves around it.
05 - Pour the white wine and stock into the pan around the lamb without pouring directly on top.
06 - Cover the pan securely with a lid or heavy-duty foil and roast in the oven for 4 hours.
07 - After 2 hours of cooking, tuck carrots, parsnips, and potatoes around the lamb in the pan.
08 - Remove the cover, increase the oven temperature to 400 degrees Fahrenheit, and roast uncovered for 30 minutes to develop a golden crust.
09 - Transfer the lamb to a platter and allow it to rest for 15 minutes before carving.
10 - Skim excess fat from the pan juices and serve the lamb with the roasted vegetables and pan sauce.