Cut the cauliflower and onions in pieces; cook them with the oil, butter, and garlic for 2 or 3 minutes. Then add enough water to cover the vegetables and cook until they are soft. Over low heat, stir in the flour, and slowly pour in the milk. Stir until the soup comes to a boil, then add the bay leaf. After simmering for a few minutes, whip the soup in a blender until light. Add the cream, reheat the soup, and serve garnished with finely chopped chives and fried croutons.