Preheat oven to 350 degreesHeat ¼ cup of the oil in a large heavy pot with cover over medium heat. Add leeks, carrots, celery, rosemary and sage and cook, stirring until vegetables are golden brown, about 10 minutes. Stir in preserved lemon, tomato paste, broth, ketchup, vinegar.Remove from heat and set aside.
Meanwhile, generousy season veal shanks with salt and pepper, then dredge in flour until lightly coated. Shake off excess flour. Heat remaining ¼ cup oil in a large skillet over medium-high heat. Add veal shanks and sear, turning once, until well browned on both sides, about 5 minutes per side. Place veal shanks in pot with vegetables, cover and transfer to oven. Cook until meat is fork tender and falling off bone, about 2 ½ hours. Serve with risotto or plain steamed white rice or mashed potatoes.