Debone a leg of lamb and trim off excess fat. Rub with salt, pepper, garlic and herbs. Tie it with butcher twine and roast in preheated oven at 400 degrees for approximately 1 1/2 hours. Let it rest for 20 minutes before carving.
Use the bones to make a lamb stock. Crack the bones and roast in oven with onions, celery and carrots until golden brown. Transfer into a pot and add 3 tablespoon of tomato paste, 3 cloves garlic, 4 sprigs of parsley, 2 bay leaves and enough water to cover the bones. Bring to a boil and then turn down the heat to simmer, skimming the fat off. Reduce to almost half its volume.
In another pot, reduce 2 cups wine, 2 chopped shallots, 5 cloves chopped garlic, and 1 tablespoon chopped rosemary to almost 1/4 of its volume and add the lamb stock. Thicken to desired consistency with cornstarch and water mixture. Adjust seasoning. Serve over sliced leg of lamb.