Egg and cream aside, what you see are the makings for a delicious and refrescantissimasso cool drink. Some living west of the Hudson River may not know of it since it is kind of a New York City thing.
One Louis Auster, a Brooklyn candy store proprietor in late 19th Century Brooklyn, New York is credited as the originator. Click for chapter and verse on all that.
The Egg Cream is the generic name since you can make it with vanilla or chocolate syrup.
Also, a key to understanding how to make a proper Egg Cream is to know that the original was a soda fountain drink; i.e., using fresh seltzer. "2 cents plain," as the expression goes. So, if you proceed on your own to duplicate this simple and refreshing beverage, think fresh seltzer; as in, open a new bottle of seltzer, please. If you have one of those fancy syphons, then the seltzer may stay longer after you charge the unit. We don't have one, so you tell us.
Here's what to do . . .
In a tallish glass fill to around one third with cold whole milk. This is not chocolate milk; most of the volume is from the seltzer.
Pour in some "Fox's u-bet" syrup. A good fat finger's width or more for a largish glass. If you can't find this brand, Hershey's will do. But, just do. Try to go old school. "Fox's u-bet" is different; and definitive for this quaff.
Not open a fresh bottle of seltzer and dump, drop, vigorous pour, earnestly introduce, cascade said liquid into your glass of milk/chocolate. This produces the mandatory and absolutely necessary creamy white foam head. You'll have to learn how much to add to prevent overflow. But, if you've seen the egg cream made at an actual soda fountain you know that overflow is usual. The mess may in fact be part of the mystique.
The with a long spoon, reach on down to the bottom of the glass and stir the milk/syrup, taking care not to disturb the foam on top.
A straw would be a nice touch. Now enjoy.
Around Passover Fox's offers a kosher version. Sweetened with sugar, not high-fructose Corn syrup. You'll know it by the seal on the cap.