In a small saucepan over medium, 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.

Stir in the butter, salt, vinegar and 1/4 heavy cream. Set aside to cool to room temperature.

Once the mixture has cooled, stir in the rum extract. This step is optional... My husband likes it better without the rum extract.

In a medium bowl, combine 2 tablespoons of the brown sugar mixture and the remaining 1/2 cup of heavy cream. Use an electric mixer to beat until just thickened, but not completely whipped, about 2 to 3 minutes.

Optional Awesome Step: Pour cream soda into medium sauce pan and bring to just under boiling.

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.

Just for adults: You can add butterscotch schnapps to each glass before topping with the whipped cream for a delicious 21+ version of this tasty treat!