The ice cream soda is a treat made, typically, by mixing ice cream with either a soft drink or flavored syrup and carbonated water, often with some special technique to encourage the partial slushing of the ice cream itself.

Invented near the end of the 19th century, it quickly became very popular, to such a degree that it was almost socially obligatory among teens, but seen as abhorrent by many adults. It was eventually banned either entirely, or on holy days, by some local governments, giving rise to the ice cream sundae.

A typical recipe:

1 tablespoon of flavored syrup

2 tablespoons of milk

1 scoop of ice cream

selzer water

glass which is wider at the top than bottom

Mix syrup with milk in bottom of glass.

Slide one scoop of ice cream into bottom of glass. Push into syrup mix and stir around a bit to make it frothy.

Add a second scoop of ice cream, then spray the soft drink down side of glass to encourage foaminess, until full.

Serve

(the more basic, modern version is to put a couple of scoops of ice cream in a glass which has a narrow bottom and wide top, add root beer, and viola: root beer float)