You will need:
1 cup (180 g) light or dark brown sugar2 tbs (30 ml) water
6 tbs (90 ml) butter
1/2 tbs (6 ml) salt
1/2 tbs (6 ml) cider vinegar
3/4 cup (180 ml) heavy cream, divided
1/2 tbs (6 ml) rum extract
Four 12-ounce bottles cream soda (I bought a 2 liter bottle and measured out 12 ounces)
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 degrees F (115 degrees C) on a candy thermometer.
|back left: cider back right: butter|
front left: heavy cream front right: salt
Set aside to cool to room temperature.
Once the mixture has cooled, stir in the rum extract.
Use an electric mixer to beat until just thickened, but not completely whipped, about 2 to 3 minutes.
To serve, divide the brown sugar mixture between 4 tall glasses (about 1/4 cup for each glass).
Then fill each glass nearly to the top with additional cream soda, then spoon the whipped topping over each.
(The colder it is the foamier is will be. If, after adding the soda, the beverage is room temperature add ice or chill before adding the foam.)