01 - Preheat the oven to 425°F.
02 - Pat the lamb dry. Use a small sharp knife to make small incisions all over the lamb and insert garlic slices into each.
03 - In a small bowl, mix rosemary, thyme, salt, pepper, and olive oil to form a paste. Rub this mixture all over the lamb.
04 - Place the lamb on a rack in a roasting pan. Roast for 20 minutes to brown, then reduce oven temperature to 350°F.
05 - Continue roasting for 1 hour 10 minutes for medium-rare, or until a thermometer inserted into the thickest part reads 135°F. Adjust time for desired doneness.
06 - Remove lamb from oven, tent loosely with foil, and let rest for 15–20 minutes before carving.
07 - While the lamb roasts, make the mint sauce: In a bowl, combine mint and sugar. Pour in boiling water, stir to dissolve sugar, then add vinegar and a pinch of salt. Let stand for at least 15 minutes.
08 - Carve the lamb and serve with the mint sauce on the side.