It's never easy to step into a role established by another actor and then make it your own.

Sierra Boggess faced that challenge taking on the role of Principal Rosalie Mullins in the Broadway adaptation of the movie "School of Rock," playing a version of the character portrayed by Joan Cusack on film.

"Joan Cusack is one of my favorite actresses, so I always loved what she did with the part of the principal," Boggess says. "I didn't want to copy anything that she did."

Boggess was able to bring a new, unique perspective to the character, who is the head of a stodgy private school that is rocked when substitute teacher Dewey Finn (Alex Brightman) enlightens them to the power of music.

amNewYork spoke with Boggess about the show.

What was your relationship with the film?

It was a film that I had seen many times, thought that it was hilarious. ... And it's one of those films that's on TV all the time.

What did you take from Joan's performance?

Once we started getting into rehearsals and everything, I didn't watch the film again for research or anything like that because I can't recreate, and don't want to recreate, what she's doing. But what I do take from somebody who's such an amazing actress is just the truth of, you have to come from a truthful place. And I think that this principal has to have some quirkiness to her. She's not a cookie-cutter -- none of them are cookie-cutter characters, and they don't want to be caricatures of anything.

Andrew Lloyd Webber, whom you've worked with before, did the music for this show. What do you like about that collaboration?

Well, obviously you're in really good hands if you're doing a show written by him. I feel very lucky -- he started my career, really, with "Phantom [of the Opera]" in Las Vegas and then continued on with many different versions of "Phantom." ... I feel like how he writes is where I want to sing. And at this point, he knows me very well and he knows my voice and he wanted to be able to showcase many different parts of my voice. And he knows me as a funny person, too, and he wanted to showcase that stuff. So, it was very nice coming into this production with him where we weren't doing the show where someone's going to die or it's terribly sad.

These kids are amazing. Did you learn anything from working with them?

I've done a few shows with children in them but it hasn't been to the degree where the children are the focus, and with this many, as well. And these kids, I've learned so much by being around them. I'm reminded to be present, in the moment. ... They are just so extremely talented and they're also great humans.

How is it performing with Alex Brightman?

Well, I feel very lucky to be in the position where I'm witnessing him step into the leading man role, and he's wonderful. He's great with these kids, it's like this part was made for him, but he never thought of it like that. He didn't think of himself as even a contender, it's just amazing. But when anyone sees the show and they see what he's doing, you're like, this part, it's like it was written for you. But everything was just perfectly aligned for him to be able to come in and showcase everything that he can do. He is just, he's incredible and I'm really, really proud of him.

Do you have a favorite moment from the musical?

Favorite moment? Oh god, there isn't a favorite; I can't pick a moment. ... I love getting to start off the show in one sort of way with my character and then I love getting into the bar scene where I can just let loose.

Your character is a huge fan of Stevie Nicks, whom you got to meet. What was that like?

Well, that was awesome. I said, on behalf of my character and myself, thank you for the inspiration. I wanted to also meet her as I was still dressed as Rosalie Mullins because I wanted the character to get to meet her. So it was amazing. I mean, she sat front row, everyone was so excited that she was there. She said that she loves the movie so much and she loved this musical, and she said that she will definitely be back.

If you go: The 'School of Rock: The Musical' has an open run at at the Winter Garden Theatre, 1634 Broadway, SchoolOfRockTheMusical.com