Jane Krakowski Butt Krak Outski For NYC Performance

0301_jane_krakowski_wardrobe_main_launchJane Krakowski put it ALL out there -- boobs and butt included -- for a lounge singer styled performance totally reminiscent of her "30 Rock" days.

Jane was the showstopper of the night at a gala for the Roundabout Theatre in NYC on Monday ... and never missed a beat when her full ass crack and nipples were exposed.

Check out the pics -- the "Unbreakable Kimmy Schmidt" star's still got plenty of Jenna Maroney left in her.