Place each rack of lamb into a large roasting dish with the garlic, rosemary, lemon zest and juice, Extra Virgin Olive oil and generous amounts of salt and freshly cracked black pepper. Rub all ingredients into the fat of lamb and cover and marinate for at least 3 hours, up to 24 hours.
Preheat the oven to as hot as it will go without the grill function (220°C).
Heat the roasting dish on a hotplate to a medium high temperature and render the fat from the lamb, browning the racks, turning the ends to brown and all sides. Allow about 8-10 minutes to do this. The garlic should be very fragrant and starting to brown as well.
Cover and place into the hot oven and cook for approximately 15 minutes (depending on the size and number of lamb racks, this could be slightly less.)
Remove from the oven, cover with foil and allow to rest 5 minutes or longer, before serving with puree and pumpkin. Drizzle all with a little of the pan juices and garnish with mint leaves.
To prepare pumpkin, peel and cut and drizzle with EVOO, pure maple syrup and some salt. Roast in a hot oven for 20 minutes until tender and caramelised. Keep hot until service.