In a Dutch oven, saute the peppers, onion and potato in oil and butter if desired for about 4 minutes or until onion is tender. Add garlic and saute for 1 minute or until garlic is tender., Stir in the broth, bay leaf, salt if desired and pepper; bring to a boil. Reduce heat; cover and simmer for 20 minutes or until vegetables are tender. , Discard bay leaf. Cool slightly; puree in batches in a blender. Return to pan. Stir in buttermilk; heat through. Serve hot or cold; garnish with sour cream and chives if desired.