01 - Preheat the oven to 425°F.
02 - Pat the leg of lamb dry. Use a sharp knife to make small incisions all over the meat and insert halved garlic cloves into each incision.
03 - Combine olive oil, rosemary, thyme, kosher salt, black pepper, and lemon zest in a bowl. Rub this mixture evenly all over the lamb.
04 - Place the quartered onions, carrot chunks, and halved garlic bulb in a large roasting pan. Position the lamb atop the vegetables.
05 - Roast the lamb at 425°F for 20 minutes.
06 - Reduce oven temperature to 350°F. Pour the white wine or chicken stock into the roasting pan. Continue roasting for 1 hour and 10 minutes, basting once or twice, until the internal temperature reaches 130°F for medium-rare or preferred doneness.
07 - Remove the lamb from the oven, tent loosely with aluminum foil, and let rest for 15 to 20 minutes.
08 - Carve the lamb and serve alongside the roasted vegetables and pan juices.