Preheat oven to 200ºC (180ºC fan-forced). Score the lamb leg three or four times in lines.

Heat the oil in a large non-stick frying pan over medium heat and cook the lamb for 3-4 minutes, turning often, until browned all over. Insert the rosemary sprigs into the scores.

Reserve 2 tablespoons of fat from the pan and place into a large bowl with the potatoes, onion and garlic. Season with salt and

Place the lamb on top of potatoes and brush lamb with half the balsamic vinegar. Cover with baking paper and foil and roast for 1 hour. pepper and toss to combine. Place in a large baking dish and pour over the stock.

Remove the foil and brush lamb with remaining balsamic. Roast for a further 40-50 minutes for medium, or until lamb is golden. Remove the lamb and allow to rest for 10-15 minutes.

Increase oven temperature to 240ºC (220ºC fan-forced), top the potatoes with the tomatoes and return to the oven for 15 minutes or until potatoes are golden and crisp.

Thinly slice the lamb and place on top of the potatoes and tomatoes to serve.