Preheat the oven to 180°C conventional oven/ 160°C fan-forced (350° Fahrenheit/Gas 4). Line a baking dish with baking paper.
Place the leg of lamb in the baking dish. Use a small sharp knife to make 6 slits over the lamb leg. Press the garlic cloves into the slits in the lamb, then drizzle over half of the olive oil. Use your hand to rub the olive oil, half of the rosemary and thyme over the lamb leg.
Roast the lamb uncovered for 3 hours, then remove from the oven.
Arrange the potatoes around the lamb. Drizzle the remaining olive oil, then sprinkle over the ariosto, and the remaining rosemary and thyme. Use your hands to gently toss the potatoes to evenly coat in the oil and herbs. Bake for a further 1 hour or until the potatoes are golden and tender.
Allow the lamb to rest, uncovered for 10 minutes. Meanwhile complete the lamb and mint gravy – buon appetito.