In a heavy, ovenproof casserole, brown the lamb in the oil. Remove the lamb and set aside. Pour off the excess fat, leaving just enough to saute the garlic. When garlic is golden, add rosemary and tomatoes. Add wine (or stock) and simmer for about 5 minutes. Return lamb to pot and season with salt and pepper. Bake at 325 degrees F for about 1-½ hours.