Pour 1.5 ounces of butterscotch schnapps over the top of the ice cream in each mug.
3 ounces butterscotch schnapps
Tilt glass and slowly pour root beer down the side; this helps to control the amount of foam. One 12 ounce can will be enough to split between two cocktails.
12 ounces root beer
Top with whipped cream, a cherry, and add a straw. You may need to scoop some extra foam off the top first.