In a small bowl, stir together the Cool Whip and butterscotch until completely combined. The Cool Whip should be a creamy white color.
Pour the chilled cream soda into serving glasses. Serve with the butterscotch topping dolloped on top. Alternatively, transfer the whipped topping to a plastic baggie and snip the corner to pipe the topping on. (NOTE: The whipped topping will start to foam when it comes in contact with the soda, do not top until ready to serve.
Serve right away and enjoy with your witch and wizard friends while marathoning Harry Potter!