I need to find this recipe... help?

[jbsegal]

"Soda fountains on the Lower East Side would mix up a batch of Droste's cocoa, egg whites, and real cream, daily. One batch each day. When it was gone, there were no more egg creams that day."
--- from a comment on http://www.wsj.com/articles/why-you-should-order-the-egg-cream-1441313172

I need to find a recipe for this syrup.