1. In a small saucepan over medium heat, combine the brown sugar and water. Bring to a gentle boil and cook, stirring often, until the mixture reads 240 F on a candy thermometer.
2 . Stir in the butter, salt, vinegar and 1/4 heavy cream. set aside to cool to room temperature.
3. Once the mixture has cooled, stir in the rum extract.
4. In a medium bowl, combine 2 tablespoons of the brown sugar mixture and the remaining 1/2 cup of heavy cream. Us an electric mixer or stir to beat until just thickened, but not completely whipped, about 2-3 mins.
5. To serve, divide the brown sugar mixture between 4 tall glasses (about 1/4 cup for each glass). Add 1/4 cup of cream soda to each glass, then stir to combine. fill each glass nearly to the top with additional cream soda, then spoon the whipped topping over each.
Here are some alternatives and ideas to experiment with
Feel free to add alcohol of your choice to make an alcoholic butterbeer. Bailey's Irish Cream is a recomended adittion. (not for underage wizards. please drink responsibly)
For the novice potion brewers out there, feel free to simply add a scoop of vanilla ice cream to a glass of cream soda, essentially making a modified root beer float.
We prefer and recomend a frosty butterbeer, put a glass in the freezer before hand to make it nice and frosty for an extra dimension. Alternatively feel free to heat the butterbeer up as an alternative to hot cocoa this winter, just be sure not to bring the mixture to a boil, you don't want to lose the carbonation in the cream soda.