Pour whipping cream into stand mixer bowl and start on medium speed. You can also use a traditional bowl and hand mixer.
Add the powdered sugar one tablespoon at a time followed by the sugar, vanilla extract and salt.
Once the ingredients are mixed in, increase the speed and whip to a slightly firm consistency. You don't want super stiff cream since this isn't for frosting.
Add the butterscotch caramel topping and continue beating to desired consistency. I try to go for something a little stiffer than Cool Whip but looser than frosting.
Spoon 1-2 teaspoons into a cold mug or glass. Pour the chilled cream soda into the glass stirring somewhat slowly with a spoon. You don't want make the two things one but stirring it will build a better head. Once the head starts to form pretty good, you can stop stirring.
Serve cold and enjoy.
Notes: You can put the unused cream into a plastic container and it will keep in the fridge for a few days. I have tested several brands of cream soda (IBC, Sprechers, Frostop) but the one that tastes the closest to what you will get at the Wizarding World of Harry Potter is definitely Boylan's Cream Soda. I use Mrs. Richardson's Butterscotch Caramel Topping and pink sea salt. I do know that the WWHP uses a non-dairy topping and I'm on the hunt for Rich's Whip Topping but no luck yet!