2.In a large flameproof dish, heat half the oil; cook lamb for about 5 minutes, or until browned all over. Add thyme sprigs; season to taste. Add potatoes, lemon and garlic to pan; drizzle with remaining oil. Roast for about 40 minutes, or until lamb is cooked as desired. Remove lamb from baking dish; cover with foil, stand for 15 minutes.
3.Meanwhile, add vegetables to potatoes in dish; toss to combine.
4.Increase oven to 240ºC (220ºC fan-forced); roast vegetables for about 20 minutes, or until tender and golden brown. Add thyme leaves; toss to combine.
5.Serve lamb racks with roasted vegetables and lemon.