01 - Preheat your oven to 430°F.
02 - Use a sharp knife to make small slits all over the leg of lamb. Insert garlic slices into the slits.
03 - In a small bowl, combine rosemary, thyme, salt, pepper, and olive oil to make a paste.
04 - Rub the herb mixture evenly over the lamb.
05 - Place the lamb on a rack in a roasting pan. Roast for 20 minutes at 430°F.
06 - Reduce oven temperature to 350°F and continue roasting for 1 hour 10 minutes for medium-rare, or until internal temperature reaches 135°F.
07 - Remove the lamb from the oven, cover loosely with foil, and let rest for 15–20 minutes before carving.
08 - While the lamb rests, mix the sugar and boiling water in a bowl until the sugar dissolves.
09 - Stir in the mint, vinegar, and salt. Let stand for 10 minutes to infuse flavors.
10 - Carve the lamb and serve with the mint sauce.