Jessie Mueller might be playing an inventive maker of delicious pies on Broadway, but she has a confession to make.

"I still haven't perfected crust. It's a butter-shortening ratio. It has to be cold," she says.

"There are a lot of things involved. The temperature of your oven, the humidity. I get lost in the chemistry."

Baking aside, the actress has definitely found the recipe for a great theater career. This month, she's following up her Tony-winning role singing Carole King songs with the lead in Waitress, which features tunes by Sara Bareilles.

"This is the kind of stuff you can't plan. That's the hand of God working," Mueller says during a grueling day of rehearsals and interviews in which she stayed remarkably buoyant. "I got really lucky."

The new musical tells the story of a waitress and pie maker trapped in a small-town diner and a loveless marriage. It's adapted from a 2007 film starring Keri Russell.

Tony Award winner Diane Paulus, the director, says it was hard to find an actress for such an emotionally rigorous role who could also sing beautifully. Mueller easily stood out.

"You feel like she rolled out of bed and here she is, a real person," says Paulus.

"She's so grounded. She's so earthy and this is a show about people who are messy, who are having challenges in their lives. She's a real person, who, by the way, can sing like nobody's business."

Bareilles, who has written such hits as Brave and Love Song, actually attended the opening night of Beautiful: The Carole King Musical, which gave her the idea that Mueller might be perfect for her musical.

Mueller now has the intimidating task of making the songs her own after Bareilles released her versions in What's Inside: Songs From Waitress, including the standout single She Used to Be Mine.

"I think it's only daunting when I think of Jessie singing the songs. But I'm not singing the songs: The character is signing the songs," Mueller says.

"The album is such a testament that these songs can stand alone as pop songs brilliantly. But you also put them into a context of a narrative and they soar, in a just different way."

For her part, Bareilles says she is ready to hand those songs over to Mueller and has even scrapped some and added a new one for the Broadway run, What Baking Can Do.

"I think if they were in less-capable hands, it would be much harder to pass the baton. But it is truly nothing but a joy to watch her interpret this material," says Bareilles.

Mueller is the third of four children raised by actors in Chicago. All of her siblings are in the business, including sister Abby who is starring as Carole King in a touring production of Beautiful.

She was initially resistant to the idea of making Broadway her career.

"I think I just wasn't really self-confident enough to feel like I could come here and have a place. It seemed like a very big, scary place to me. I was like, 'Oh, I don't look right' or 'I don't sound right'."

Mueller made her Broadway debut in 2011 in On a Clear Day You Can See Forever with Harry Connick Jr and went on to replace Kelli O'Hara in Nice Work If You Can Get It and starred in The Mystery of Edwin Drood.

Her Tony for Beautiful was especially sweet considering her wariness.

"I feel really fortunate that all the things I felt early on that I thought would make it hard for me to work are actually the things that have made me more unique," she says.

Jessie Mueller takes a bow onstage during the opening night of Beautiful: The Carole King Musical in New York City in this file photo from 2014.Getty Images