“Waitress: The Musical” (***1/2 out of four) was a dazzling musical adaptation of Adrienne Shelly’s 2007 cult smash about a small-town waitress (Sara Bareilles) who works through her frustrations at a diner in the South and begins an affair with her new doctor (Drew Gehling) and dreams of a way out to a new life. Glitzy production numbers performed by a bright and high-spirited cast make this a heartfelt smash and a rare musical that significantly adds to (and improves on) the initial film it was based on; kudos to Scott Pask’s colorful and eye-catching production design and Bareilles who is wonderful in the lead. Goes on a bit too long but never fails to keep you entertained.