From the Back Cover:
If you’re a behind-the-scenes type, you might be interested to know the making of this album represented one of the shortest recording sessions in album history. Steve showed up at the date without having decided what tunes he wanted to do. From there on in, Allen, working with his shirt off for most of the session, just called them off and played them. That’s pretty much Steve’s approach to television and life, too. He ad-libs it.