Sauté onion in butter in a medium saucepan until tender. Add 2 cups chicken broth and curry powder; bring to a boil. Reduce heat; simmer, uncovered, 15 minutes. Remove from heat; stir in rice.
Pour rice mixture into container of an electric blender, and process until smooth.
Combine cauliflower and remaining chicken broth in a large Dutch oven; bring to a boil. Reduce heat; simmer, uncovered, 15 minutes or until tender. Stir in rice mixture, whipping cream, salt, and pepper. Serve in individual soup bowls.