01 - Preheat the oven to 400°F (200°C).
02 - Pat the leg of lamb dry with paper towels. With a sharp knife, make small incisions all over the lamb and insert garlic slices into each.
03 - In a small bowl, mix rosemary, thyme, salt, pepper, olive oil, lemon zest, and juice. Rub this mixture all over the lamb.
04 - Place the lamb on a wire rack in a large roasting pan.
05 - Toss the potatoes with olive oil, salt, pepper, and rosemary. Arrange them around the lamb or in a separate roasting tray.
06 - Roast the lamb and potatoes for 1 hour 20 minutes for medium-rare (internal temp: 130–140°F/55–60°C), or to your desired doneness, turning potatoes once halfway.
07 - If desired, during the last 20 minutes, pour stock into the pan to create a light jus.
08 - Remove lamb from the oven, tent loosely with foil, and rest for 15–20 minutes.
09 - Increase oven to 425°F (220°C) and return potatoes to crisp up until golden, if needed.
10 - Slice the lamb and serve with roasted potatoes, drizzled with any pan juices and sprinkled with fresh parsley.