In a large pot, combine potatoes, carrots, celery, turnip, onion, parsley, salt, and pepper. Cover with water and simmer for 30 minutes or until vegetables have softened.
Meanwhile, in another saucepan, melt butter and stir in flour. Add a small amount of liquid from the large pot of vegetables to form a paste.
Cool the paste and stir in milk and sour cream.
When the vegetables are fully cooked, mash or purée them and incorporate the flour-milk mixture. Heat the soup but try to avoid a boil.
Serve sprinkled with bacon, shredded cheese, and chives, if desired. Delicious served hot or cold, this soup can also be made in advance and frozen until ready to eat.
