CAMBRIDGE (CBS) – She has sold more than a million albums and more than seven million singles.

VH1 lists her in the top 100 of women in music.

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By any measure, Sara Bareilles is a major star.

Now she is lending that immense talent to the stage. The 35-year-old singer-songwriter has written her first musical, called “Waitress,” based on the 2007 film. It will open this month at the American Repertory Theater in Cambridge.

It’s a story of a young woman caught in a loveless, abusive marriage.

Bareilles spoke to WBZ-TV’s Liam Martin and Paula Ebben recently at the A.R.T.

Sara Bareilles talks to WBZ-TV's Liam Martin and Paula Ebben. (WBZ-TV)

Sara Bareilles talks to WBZ-TV’s Liam Martin and Paula Ebben. (WBZ-TV)

SARA: I always, when I imagined my life, I thought I would be on stage — but on the theater stage. So it was a little bit of a left turn to realize that songwriting became so important to me.

LIAM: You were initially intimidated by the prospect of writing a musical. You are obviously a major star in music. Why were you intimidated by this?

SARA: I grew up on musical theater. I think have so much respect for the legacy of this medium. You don’t want to try your hand at something this publicly, and then just have it be awful (laugh). I can’t wait. We’ll have an audience within a week. I can’t wait to see what resonates with them. It’s a little terrifying, but it’s a huge blessing to see the show come to life before taking it to New York, hopefully – fingers crossed.

PAULA: Your fans know you primarily as a soulful songwriter, and all of your songs are a little story, like a vignette within the song. Did you feel at home when you started writing the songs?

SARA: I felt coming to this genre felt like a homecoming to me in some ways, because musical theater is part of the reason why I write the way I do. I grew up listening to musical scores, and so I loved getting introduced to a character by way of their torch song or understanding some deeper aspect of their soul or their story or their history by way of the songs that they were given to sing.

LIAM: Tell us about the musical. Tell us the gist of the story, and how you wrote the music around that.

SARA: It’s about the lead character, Jenna, a brilliant pie-baker, who sort of tucks her emotions and most inner thoughts into her pies, and she sort of feeds the soul of the community by way of her pies. And she’s in a strained and loveless marriage. It’s really her story about coming to terms with what she’s not and what she hopes to see herself become, and finding the strength to sort of step out on her own.

LIAM: One of the songs, which is my favorite so far, ‘She Used To Be Mine’ — will you tell us about that song? Is it a reflection on the past self?

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SARA: I have a penchant for melancholy myself. And when I watched the film, I was really struck by the scene where Jenna and her husband, Earl, are in the kitchen. And it’s her bottom-of-the-well, darkest moment. I think everyone can relate to the feeling of waking up and seeing their lives having happened around them and almost wondering, ‘How did I get here?’ And what do you recognize about yourself and what don’t you, and who were you, and who did you think you were going to be? So that kind of encapsulates the song there.

PAULA: People think, ‘Oh, it’s a musical.’ But there are some really strong themes in it.

SARA: There’s a lightness to it and a sweetness to it, but it’s also not afraid of what is melancholy about life, and what is lonely and dark about our experience here. And I think that these characters illustrate it beautifully, and I’m really proud of what we pulled together here.

LIAM: Domestic abuse is definitely a theme throughout the musical. How did you tackle that through the music?

SARA: Delicately. I think we are trying to be very mindful of how we portray that experience. It’s just not black and white. I think we’ve done a good job of shading this in a way that you can understand why someone ends up in a position where, from the outside, you’d be like, ‘Just get out of there!’ But it’s not that simple a lot of the times.

PAULA: You’re such a strong female voice. Is it hard to write for men — male characters?

SARA: Totally. It’s hard to write for men. I made many mistakes along the way — just from a technical aspect of writing songs in keys that were way too high for them to sing. They’re like, ‘We’re men. Our voices are lower than women,’ so learning moments for me. I took it as a great challenge to find what I could empathize with inside of each of these characters, and how I recognized myself in them.

LIAM: Jenna is the main character. She’s definitely complicated. Would you say you found yourself in her? Is the music somewhat autobiographical?

SARA: Absolutely. I deeply fell in love with Jenna. ‘She Used to be Mine’ — I hear that song now, and it still makes me cry. That doesn’t happen very often. Part of it is because Jessie Mueller is singing it, and she is our lighthouse; she is an incredible, incredible gift to this production. But I understand Jenna’s story so deeply, and it made it easier to find my way into this type of storytelling.

PAULA: What do you want to say to people about coming to the A.R.T. and seeing it and giving it a try?

SARA: I say, come open-minded and hopefully leave open-hearted. This show is about intimacy and about small storytelling, and hopefully done with music that makes you feel uplifted and open-hearted.

LIAM: What’s next for you? You’ve now written a musical. You’re VH1 top 100 women in music. You’ve kind of done it all. What’s next?

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SARA: Umm …. maybe a vacation? (laughs)