I'm amazed and excited to discover something chowhoundish near Rock Center.
Minamoto Kitchoan (608 Fifth Ave. at 49th) 212 489 3747 is a little bit ridiculous at first glance. A ground floor place, with incredibly expensive real estate, it looks like a jewelry store. Then you notice it's a bakery--with everything they sell flown in from Japan (a shipment arrived while I was there).
Get the daifuku (as much fun to eat as it is to say.) It's a small white pillow of soft marshmallow-like rice, filled with bean paste. Unlike the daifuku I get from my korean deli, though, this isn't sweet like candy. It's ethereal sweet, barely sweet, delicious.
They have a ton of other weird stuff which I intend to work my way through. Even though I'm a complete gaijin, the folks behind the counter couldn't have been nicer.