Trim fat from beef shanks. In a large Dutch oven or kettle combine meat, water, bouillon granules, salt, and pepper. Place parsley, celery leaves, bay leaves, garlic, and thyme on a 10� square double thickness of 100-per-cent-cotton cheesecloth. Tie into a bag with a clean string; add to Dutch oven. Bring to boiling; reduce heat and simmer, covered, for 2 hours.
Remove meat from soup; set aside to cool. Cut meat off bones and coarsely chop; discard bones. Skim fat from broth. Stir chopped meat, tomatoes, sweet potatoes, parsnips, carrot, and celery into broth.
Return to boiling. Reduce heat and simmer, covered, for 15 minutes. Stir in pea pods; simmer, covered, for 1 to 2 minutes more or until the pea pods are crisp-tender. Remove cheesecloth bag and discard. Ladle soup into bowls.
Make-Ahead Tip: Prepare soup but do not add pea pods. Pour soup into a storage container. Cover and refrigerate up to 24 hours ahead. To serve, transfer mixture to Dutch oven. Cook over medium-low heat until heated through. Add the pea pods and simmer, covered, for 1 to 2 minutes or until pea pods are crisp-tender.