This trick is a variation of a Straddle Whip and can be performed both at the front and the backend.
Hold the bar in a wide grip and as you get up into the Straddle Whip position, drop your butt between your arms. Your legs can be straight if you are very flexible, or bent (in the position that inspired the name 'Croissant').
Thanks to Rachel for providing a video for this page and Maria @m_knf for providing the inspiration and allowing us to share her demonstration of the position.