Roughly chop the jaggery and the tamarind. Add about 150 - 200 ml of hot boiling water to the mixture to make the jaggery melt and create a thick gravy type paste
Finely chop the mint leaves and add to the jaggery mixture
Wash the leg of lamb and score it. Rub in the salt, pepper and sambhar masala
Coat the entire leg with the jaggery-tamarind marinade. Allow the leg to marinate for atleast 2 hours at room temperature or ideally overnight in the refrigerator
Preheat the oven to 200 degrees celsius
While the oven is heating, prepare your vegetables by peeling the sweet potatoes and carrots and quartering all of them. Also, peel and chop the onion in eights and crush the garlic with the peel on
Heat a big pan on the stove and add in the ghee. Place the entire leg of lamb in the pan allowing the skin to sear and brown
Remove the lamb and place in a roasting tray. In the same pan, add in your vegetables and cook them uncovered for about 5- 10 mins - this is just to allow them to soak up the juices from the meat
Assemble the leg of lamb in the centre and the roast vegetables around it. Cover with foil and place in the oven for 35 - 40 minutes
Serve immediately with a mixed green salad