When Joanie, John and the kids came to visit us in New York, one of their favorite treats was a chocolate egg cream. We tried this one at the diner, then made them at home.
This Jewish/NYC tradition contains neither eggs nor cream, but at least it has chocolate!
A quick squirt of chocolate syrup, then about 3/4 cup of milk, then a cup or so of seltzer. Then beat it like mad with a spoon to whip up foam, then fill the rest of the way with seltzer.
Keep on beating with that spoon, and it'll come up real light and creamy.
We tried making it with soy milk, but the foam turned kind of messy.