In 2007, Sara Bareilles told her record label, “I’m not gonna write you a love song,” but when she was asked to pen a Broadway musical in 2013, she leapt at the chance.

“I had left Los Angeles, my home of 14 years, I had just moved to New York City, I didn’t really know many people, and I was having a mini midlife crisis. Everything about my life was in major flux. I said yes to this project almost as an experiment. I didn’t really even think I could do it. I want to give a lot of credit to my wonderful collaborators in crafting the seeds of these ideas so I could go to my cave and start writing songs about it.”

The result was Waitress, a Tony-nominated smash on Broadway before launching a national tour that’s currently playing at the National Theatre (15 May – 3 June). Based on the 2007 film by Adrienne Shelly and adapted by Jessie Nelson (book) and Bareilles (music, lyrics), the story follows Jenna, a small-town waitress and expert pie maker who’s stuck in a loveless marriage until a baking contest and unexpected romance with the town doctor offer her a fresh start.

“We were working mainly just from the script at first from the movie, but when I met Jessie, we became fast friends. It was one of those soul-mate relationships where I met her like, ‘Oh! I feel like I’ve known you my entire life!’ We worked really well together. One of the things I’m most proud of is I feel like the dialogue and songs really speak to each other. It’s not one of those shows where you’re like, ‘I see a song coming. Here comes the song.’ We worked very hard to make the scenes support the song, and the songs support the scene.”

This is evident right out of the gate, as “Opening Up” works on multiple levels: (a) opening up the show, (b) opening up the restaurant, and (c) opening up the protagonist’s emotional arc.

“I wanted to set a tone. I wanted it to have energy and lots of room for lots of voices to sing because we have a big ensemble. Actually, fun fact: I rewrote the opening number probably about 30 times! We had such a hard time cracking it. The day that we finally got it, oh my god, I almost burst into tears. We were days before opening and kept changing the song over and over and over again. It was so intense to get to the end result.”

That lends a little irony to the song’s lyric “some things never change.”

“Some things only change! Our Broadway cast learned so many different versions of that song that they wanted to murder me by the end. The whole chorus – ‘Hello, how ya been? Thank you, come again’ – that all got added late in the game. I was sitting in the back room in our theatre, we were in rehearsals just days or weeks before opening for preview audiences, and I finally wrote a new section and everything clicked.”

“The ‘sugar, butter, flour’ loop came really early. These little vignettes are us going into her mind, her little dream state. The illustrations came from our choreographer Lorin Latarro, who read an article in The New York Times about the importance of daydreaming, how it keeps our creative minds vibrant and alive. She’s like, ‘What if we watch her actually daydream and we watch them come to life?’ They’re really effective moments in the show.”

Not only is the show symbolic, it’s also wonderfully silly. This is especially true in the role of Ogie, who provides comic relief as the eccentric love interest of Jenna’s shy coworker Dawn. “He’s just a sweet, kind, earnest weirdo that you just fall in love with. He’s a total showstopper. That’s all Jessie Nelson. She came up with the adorable conceit that they were Revolutionary War fanatics, which is really funny!”

While Ogie’s number “Never Ever Getting Rid of Me” makes us cry laughing, Jenna belts the tear-jerking ballad “She Used to Be Mine,” filled with nostalgic, introspective lyrics: “She is messy, but she’s kind / She is lonely most of the time / She is all of this mixed up and baked in a beautiful pie / She is gone, but she used to be mine.”

“That was actually the first song I wrote. I was really struck with this idea that we all become a different version of the person we thought we would be. It’s reconciling who did you think you’d grow up and become, then when you look in the mirror, what do you see? I was dealing with that in my own life and channeling it through Jenna. That demo came out first thing. It didn’t change at all. I didn’t rewrite that song 30 times like the opening number.”

“I was lucky enough to be in the role on Broadway twice and one of the traditions of Broadway is old-fashioned fan mail. I got letter after letter from people who were transformed or transfixed by the story and changed in some way. It was really overwhelming. I remember one day I was responding and I was just in my dressing room weeping from the generosity of these fans who are so honest and so beautifully connected to the material.”

She recently met these fans in person for “Cast Album Karaoke” at National Theatre, as D.C. audience members were invited up on stage after the show to sing with Bareilles on 25 May.

“It was one of my favourite things. Once a month we do ‘Cast Album Karaoke,’ where audience members get called up and get to sing songs from the show with the actual Waitress band. It’s so magical. Sometimes you get people who have never been on stage before and aren’t real singers, and sometimes you get people who bring the house down.”

You can participate in the next “Cast Album Karaoke” on 1 June. Bareilles will be in New York, prepping to host the Tonys, but you can sing along with the talented cast, led by Desi Oakley.

“What we tried to do with this show is make something that had a lot of heart. Especially right now in the world, it’s so nice to see a show that’s about relationships, good people making mistakes, doing the best they can. It really was built with a lot of love.”