Slice first 3 ingredients; saute in oil in a Dutch oven until tender. Stir in broth; bring to a boil. Add cauliflower; cook, stirring occasionally, 15 minutes or until tender.
Process soup in batches in a blender until smooth; return to pan. Stir in cream, salt, and white pepper; cook over low heat, stirring often, until thoroughly heated. Ladle into bowls, and garnish, if desired.