Grab the milk and ice cream ....
Pour 3oz of chocolate syrup in a large fountain style glass.
(Gourmets and Purists always used to use the Kosher for Pesach Ubet which is sugar only and considered the finest chocolate syrup available. I have not used it in years however and have no idea as to its kosher status now.)
Fill the glass nearly half full with icy cold seltzer or club soda and stir it very well.
Add 1 or 2 scoops vanilla ice cream and watch the foaming begin.
Fill with more ice cream if you can manage it and top with Whipped cream.