Melt butter in soup pot , add celery ,leek + onion. Cook slowly ,covered, stirring often(about 10 minutes) ,don’t let it brown . Add broth and bay leaf simmer 10 minutes. Add potatoes 10 to 15 minutes or until potatoes are tender . Remove bay leaf. Put about 1/3 of soup in a blender ,wait a minute or 2 for it to cool them blend till smooth. Add back to soup, season with salt and pepper and garnish with chopped celery laves. Creamy and delicious.