01 - Set the oven to 300°F (150°C) to prepare for slow roasting.
02 - Pat the leg of lamb dry with paper towels and make small slits all over using a sharp knife. Insert sliced garlic cloves into each slit.
03 - Combine olive oil, rosemary, thyme, lemon zest, lemon juice, kosher salt, and black pepper into a paste. Rub this mixture evenly over the lamb.
04 - Place carrots, onions, and potatoes (if using) in a large roasting pan, forming a bed for the lamb.
05 - Set the lamb atop the vegetables and pour the white wine or chicken stock into the pan base.
06 - Cover the lamb loosely with aluminum foil and roast for 3 hours to develop tenderness.
07 - Remove the foil and continue roasting for 45 to 60 minutes, basting once or twice with pan juices until lamb is deeply browned and fork-tender.
08 - Transfer the lamb to a cutting board, loosely cover with foil, and allow it to rest for 20 minutes to redistribute juices.
09 - Carve and serve the lamb alongside the roasted vegetables, drizzled with pan juices.