The new musical is based on the film by Adrienne Shelly.
Seth MacFarlane, Sara Bareilles, Pentatonix, and more will also be on hand to celebrate the holiday season at Christmas in Rockefeller Center.
Waitress is expected to premiere at American Repertory Theater.
But first he's getting casual with Seth Rudetsky as part of Provincetown's Broadway @ The Art House concert series.
Jerry Seinfeld, Bernadette Peters, and Clive Davis were also on hand to cheer for Jessie Mueller and the cast of the new musical.