In a heavy soup kettle, melt butter. Add oil. Add onion, scallions, and garlic. Add celery and cauliflower. Add seasonings. Mix well and cook, uncovered, over medium heat for several minutes, stirring frequently.
Add chicken broth. Bring to a boil. Simmer, covered, over medium heat for 15 minutes or until cauliflower is tender. Remove cover and cool slightly.
Puree in small increments in blender until smooth and creamy. I leave small chunks of cauliflower.