echo Nick Solares in his thoughts on the bun, (Although I'm not as bothered by the burgers arriving cut in half, I find them plenty juicy and easier to eat that way. It also adds some visual appeal as soon as the burger hits the bar.) The bun is perfectly sized and of appropriate heft to support but not detract from the beef. As he is more eloquent than I, I'll quote his heartfelt feelings:
The bun, whose provenance Capon rightly refuses to divulge, might just be the best I have ever had on a burger. It is soft, airy, and squishy. The exterior has a beautiful golden hue and the interior is as pure in color as the driven snow. It conforms around the patty holding it snugly in a pillowy embrace. It is not quite a flavor neutral a supermarket bun having a mild yeastness and a hint of sourness.Nick's got way better pictures over there as well if you want more burger porn, but here's a shot that poorly shows the generous blanket of truffles and the juicy burger soaking into the bun.
The place is apparently packed most evenings; the bartender mentioned the bar routinely gets 4 deep. I happened to be in the area one afternoon and wandered in for a leisurely lunch, grabbing a seat at the sparsely occupied bar. If you like avoiding crowds as I do, this is the recommended play and makes for a pleasant lunch.
They plan to run the burger special until mid Jan or so, or however long the truffles are available. If you are interested in giving it a try keep that in mind.