1. Sauté all chopped vegetables but potato in butter until translucent.
2. Add Sherry and cook until liquid evaporates.
3. Add 5 cups stock and potato. Simmer until potato is tender.
4. Puree soup in blender or food processor.
5. Return to pot and heat thoroughly. Use extra chicken stock to thin if necessary.
Garnish with chives and croutons.