Where we've featured it
Cafe Zaiya has two locations on 41st Street. The one you need to know about (for soft serve purposes) is between 5th and Madison, and has very good black sesame and matcha flavors that come in big portions.
This Japanese deli sells everything from rice bowls to sushi, but you should be coming mainly for two things: soft serve and onigiri rice balls. The soft serve comes in green tea and sesame flavors, and a swirl of the two both tastes and looks great. The rice balls (try the spicy salmon or shrimp tempura) come wrapped in such a way that the seaweed stays crispy, like a fresh handroll at a sushi bar. It's key, and so is Cafe Zaiya in your Bryant Park lunch routine.