vanilla ice cream
root beer / cream soda
Half fill two glasses with root beer, place a generous scoop of ice cream into the glasses and
top with root beer.
Pour the root beer slowly over the ice cream as the combination of the two will create a very tall foam head, which is exactly what your after.
Notes: I haven't given amounts for the ingredients because quite frankly I think this depends on both the glasses you use and your tastes. I tend to use one large scoop of ice cream and one can of soda per person in tall glasses.