In soup pot or Dutch oven over medium high heat, saute onion in butter until translucent and just starting to brown. Add broth and zucchini. Simmer until tender, about 15-20 minutes.
Working in batches, carefully spoon soup into a blender. DO NOT FILL BLENDER PAST 1/2 FULL; THE HOT SOUP WILL EXPAND AND CAN BLOW THE LID OFF. Cover the lid with a kitchen towel and puree soup. Pour soup into a serving bowl and repeat until all soup is pureed.
Stir in whipping cream. Soup can be served hot or cold. Garnish with Parmesan cheese and parsley flakes. Makes 6 servings. Enjoy!