Rosemary Leg of Lamb with Parsnips and Onions

Peel and coarsely chop the onions, carrots, celery, and parsnips. Rinse the lamb and pat dry, and season to taste with salt and pepper. Heat the oil in a pan, and sear the lamb on all sides. Remove the lamb from the pan, and sauté the onions, carrots, celery, and parsnips. Add the pressed garlic cloves and the tomato puree and sauté briefly. Deglaze the pan with the red wine and the lamb stock. Brush the lamb with the rosemary mustard, then place on top of the vegetables. Add a sprig of rosemary to the pan, and roast in the oven for 2 hours. Baste the lamb occasionally with the liquid in the roasting pan. Remove from the oven, then season the sauce in the pan with salt and pepper. Arrange the lamb and the vegetables on a platter, garnish with rosemary, and serve.