Melt butter in saucepan; add onion and celery and cook until tender. Wash and trim broccoli; cut into small pieces. In a large saucepan, add broccoli and bouillon. Bring to a boil; cover and cook over medium heat for 20 minutes. Stir in onion and celery. Puree 2-3 batches in blender or food processor. Return to saucepan, add cream and cook 2 minutes until thickened. Garnish with chopped scallions.