01 - Preheat your oven to 400°F.
02 - Pat the leg of lamb dry. Using a sharp knife, make small incisions all over the meat and insert garlic slices.
03 - In a small bowl, mix rosemary, thyme, salt, pepper, olive oil, and lemon zest. Rub this mixture over the entire lamb.
04 - Scatter the onions over the base of a large roasting pan. Arrange the potatoes around the sides. Place the lamb on top of the onions.
05 - Pour the white wine and stock into the pan, avoiding direct contact with the lamb's crust.
06 - Roast uncovered for 20 minutes at 400°F.
07 - Reduce oven temperature to 350°F and continue roasting for about 1 hour 20 minutes (approximately 20 minutes per pound) for medium-rare, turning the potatoes once or twice for even browning.
08 - Baste the lamb with pan juices halfway through roasting. If potatoes brown too quickly, shield them with foil.
09 - Once the lamb reaches your desired doneness (internal temp 130-140°F for medium-rare), remove from oven. Cover loosely with foil and rest for 15 minutes.
10 - Carve the lamb and serve with roasted potatoes and onions, spooning over pan juices.