For the Sweet Cream Layer: In a mixing bowl, combine the heavy cream and powdered sugar. Using a whisk or an electric mixer, vigorously whip the cream and sugar until soft peaks form. Set aside.
For the Butterscotch Mixture: In a microwave-safe bowl, heat the butterscotch syrup and unsalted butter together until the butter is melted. This can also be done on the stovetop over low heat. Stir the mixture well to ensure the butterscotch syrup and butter are fully combined. Allow it to cool slightly.
For the Assemble the Butterbeer: Take your serving glasses and pour the butterscotch mixture into each glass, distributing it evenly among them. The butterscotch mixture will settle at the bottom of the glass. Open the bottle of cream soda and pour it slowly into each glass, over the butterscotch mixture. Leave a little space at the top to accommodate the sweet cream layer. Gently spoon or pipe the prepared sweet cream over the top of each glass, creating a frothy and creamy layer. For an extra touch of authenticity, you can serve your Butterbeer with a colorful paper straw or even a drizzle of extra butterscotch syrup on top.