Start by making the butterscotch base. Add the brown sugar and water to a pan, and gently simmer until the sugar has completely dissolved. Stir in the butter, syrup, and salt and mix well. Set aside and allow to cool. You can refrigerate it for a couple days, but bring to room temperature before using. It will be very thick! 

Next, prepare whipped cream. Add all the ingredients into a bowl, and whip with either a mixer or immersion blender. Whip until the cream is thick with stiff peaks. 

And now you're ready to make the butterbeer! 

In a 16 oz mug, mix 1/4 of the brown sugar butterscotch with cold cream soda. Stir until it's well blended. Top with whipped cream and enjoy! But I bet you won't drink just one glass!