Measure 1 1/2 teaspoons butterscotch topping syrup into each mug (chilled mugs work great).
Add 1/4 cup of cream soda into each glass and stir with a spoon until butterscotch topping is completely mixed in with the soda. Set aside.
Combine Reddi-wip, remaining 1 1/2 tsp. of butterscotch syrup, and 1/2 Tbsp. of cream soda in a small bowl until well combined.
Pour remaining cream soda into mugs. Spoon foam mixture on top of each drink.
You can enjoy this right away or let stand 1- 2 minutes to get the full effect and look of the Wizarding World of Harry Potter butterbeer. Enjoy!