1. Preheat the oven to 175°C (350°F). Lightly rub the skin of the leg of lamb. Season the inside and outside with salt and pepper. Peel and chop 3 cloves of garlic. Stuff the leg of lamb with the chopped garlic, distributing it evenly, and half of the rosemary, before closing the meat. Tie the leg of lamb with kitchen twine. Using a sharp knife, make incisions in the flesh and insert the remaining cloves of garlic. Sear the leg of lamb until nicely browned.
2. Mix the ingredients for the glaze. Place the leg of lamb in a baking dish. Pour olive oil over it and massage the meat with your fingers to make it penetrate. Place the remaining rosemary on top, then put it in the oven. Cook for 1 hour and 20 minutes (the leg of lamb is cooked when the internal temperature reaches 64 to 65°C or 147 to 149°F). Regularly baste with the cooking juices. Brush the leg of lamb with the glaze several times towards the end of cooking, and once after removing the dish from the oven. Let it rest for 15 minutes, covered with parchment paper, before carving the meat.
3. Preheat the oven to 225°C (450°F). Wash, dry, and cut the sweet potatoes into quarters. Place them on a baking sheet lined with parchment paper, drizzle with a little oil, and toss to coat. Bake for 20 minutes on the middle rack. Flip the sweet potatoes halfway through cooking. Season with salt after removing from the oven.
4. Cook the green beans in boiling salted water for a few minutes.
5. Slice the meat and serve it with the sweet potatoes and green beans. Serve the remaining glaze in a separate bowl.