01 - Preheat the oven to 400°F.
02 - Pat the leg of lamb dry with paper towels. Using a sharp knife, make small incisions all over the lamb and insert garlic slices into each cut.
03 - Rub the lamb with 2 tablespoons olive oil, rosemary, thyme, salt, and pepper.
04 - Place the lamb in a large roasting pan. Scatter potatoes and onion around the lamb. Drizzle the remaining olive oil over the vegetables and toss to coat. Season potatoes with a little extra salt and pepper.
05 - Pour the wine and broth into the bottom of the pan, avoiding pouring directly over the lamb.
06 - Roast in the preheated oven for 30 minutes at 400°F.
07 - Lower the temperature to 350°F and roast for another 60 minutes, basting occasionally with pan juices.
08 - Check the internal temperature of the lamb: 135°F for medium-rare, 145°F for medium.
09 - Remove the lamb and potatoes from the oven. Rest the lamb, loosely covered with foil, for 15 minutes before carving. Serve slices of lamb with the roasted potatoes and pan juices.