1 c light or dark brown sugar
2 T water
6 T butter
½ t salt
½ t cider vinegar
¾ c heavy cream, divided
½ t rum extract
4 - 12 oz bottles cream soda
In a small saucepan over med 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.
Stir in the butter, salt, vinegar, and ¼ c heavy cream.
Set aside to cool to room temperature.
Once the mixture has cooled, stir in the rum extract.
In a medium bowl, combine 2 T of the brown sugar mixture and remaining ½ c of heavy cream.
Use an electric mixer to beat until just thickened, but not completely whipped, about 2-3 mins.
To serve, divide the brown sugar mixture between 4 tall glasses (about ¼ c for each glass).
Add ¼ 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.