Mary Poppins Returns is the movie Marc Shaiman and Scott Wittman have been waiting for

Throw a dart at your DVD or Playbill collection and whatever you hit, Marc Shaiman was probably involved in it.

The composer and his songwriting partner, Scott Wittman, form a duo responsible for a host of titles that have become cherished parts of any musical fan's menagerie: Hairspray, the huge 2002 Broadway and movie hit; Smash, NBC's gone-but-not-forgotten 2012-13 backstage dramedy; the recent Broadway adaptations of Catch Me If You Can and Charlie and the Chocolate Factory; and countless awards shows in between. Individually, Shaiman has lent his solo talents to bringing evocative musical life to everything from Sister Act, Beaches, and the South Park movie to The First Wives Club, When Harry Met Sally, Sleepless in Seattle, A Few Good Men, Misery, The American President, The Bucket List… and look, just head here and get your Spotify search ready.

All of it is to say that there's been no lack of revered projects shared between Shaiman, 59, and Wittman, 63. But despite their pedigree, both men still identify as fans at heart who have admired and consumed the great pop culture before them—meaning that when the opportunity arose to potentially write music for Disney's Mary Poppins Returns, director Rob Marshall's sequel to the 1964 classic, Shaiman and Wittman might as well have been wide-eyed kids freshly new to New York City for how eager they were to get their foot in the studio door.

"I had the emotion of truly not knowing — and this isn't just rhetoric — I didn't know what I would do if we didn't get this job," Shaiman tells EW, discussing Mary Poppins Returns for EW's cover story. "Once I knew it existed and we were up for it, I truly was, like, really in need of psychiatric… I mean, I would have been… I mean, I didn't know what I would do if we didn't get it. I was truly thinking, I will have to move to a hut in Tahiti. I won't be able to live in a world where this movie comes out and we didn't get to do it. So even with the fear of taking it on…"

Wittman chimes in: "It was scarier not taking it on."

That's because Mary Poppins Returns is not just a gig to Shaiman and Wittman; it's a lay-all-your-cards-out title that marks the high-profile culmination of their ascension as musical theatre's A-list composers, and in some regards, the peak of their musical style, too. And while the film stands to help them reach their biggest audience yet on a worldwide scale, it also affords the pair the personal chance to live out nothing less than a lifelong dream behind the scenes.

"The kind of music and style that I most ever wanted to write for a movie was just finally right in front of me," says Shaiman, equating scoring Mary Poppins Returns to finally finding an outfit that fits right off the rack (and if you like that metaphor, you'll love the music). "I'm certainly writing in a style that you don't quite hear anymore. I mean, I was so well-suited for this movie because I'm sure there are other directors over the years who have walked away from a scoring session of mine and said, 'Why is this schmuck scoring my movie like it's a Mary Poppins movie?' And finally I actually was scoring a Mary Poppins movie."

But the love for the music of 1964's Mary Poppins — with its songs by Richard and Robert Sherman and its score by Irwin Kostal — wasn't just an accidental bonus; it helped the pair get hired in the first place. Producer Marc Platt, the prolific musical-minded producer behind Wicked, La La Land, Into the Woods, and dozens more, knows well the resume of Shaiman and Wittman (as does director Marshall). Platt says the musicians' pure love of the 1964 filmmade them the clear frontrunners for the job. "Where Marc and Scott really won the day, beyond their obvious talents as songwriters, is that they both came from a very emotional place," recalls Platt. "Particularly Marc, I think, really felt that his love of music and musical film came from the Sherman Brothers, and it lived in such a deep place in him. His and Scott's craftsmanship, and that emotional connection, was undeniable to us." Shaiman offers no argument: "This entire movie… is a love letter to the Sherman brothers and to all the other filmmakers on Mary Poppins and it was our way of really saying thank you to them. That's what it is. It's just a big f—ing thank you letter to all of them."

Once Shaiman and Wittman landed the job, the task at hand was to create new songs (and, for Shaiman, an entire score) that matched the sensibility of 1964's film but stood alone as something singularly original. In songwriting, they had the benefit of already knowing that Emily Blunt would be playing Mary Poppins, the marvelous nanny who returns to Cherry Tree Lane to help a now-grown Jane (Emily Mortimer) and Michael Banks (Ben Whishaw) in 1930s London; moreover, the writers knew that Lin-Manuel Miranda, a Broadway mainstay himself, would be making the transition to film playing an original character named Jack, the heir apparent to Dick Van Dyke's Bert. "All these songs were bespoke on Emily and Lin, so we had the luxury of having them there to sing every version of everything, which was a big key for us getting into the characters," says Wittman.

With Miranda, who gets to rap (or something like it) in two songs in the film, it was a no-brainer to give the Hamilton star a selection of songs that showcased his verbal dexterity, but Miranda's wish to join the film strictly as an actor — and not a songwriter or composer — added an extra layer of responsibility. "The reason he took the job was to, specifically, be an actor and a performer and exercise that part of him," says Shaiman. "So we all, Rob included, had to have confidence in our choices of how to present Lin. How much of what people would expect or want from him, to make sure it's in there, but also to make sure that we weren't pandering and we were giving him the chance to show other sides of himself." (The experiment paid off, Miranda tells EW: "One of the most fun things for me as a songwriter who didn't have to write any songs was just being along for the ride watching Marc and Scott work. I learned a bunch. Scott had all these books, these thesauri of British-isms, literally piled knee-high, with arcane sayings like 'A real pea souper!' It was really fun just watching them go through and craft that.")

Blunt, meanwhile, informed not just the reimagined character of Mary Poppins but the film's internal production in general. Wittman recalls, "She would come once or twice a week and we'd try this on her, try that on her, and it was so singular to her. She had created this very confident, witty woman, which is what she is as a person, but it also freed up, for us, that version of Mary." Shaiman points out, "Her courage was contagious — or her confidence, I should say. Can you imagine stepping into this role? One of the most iconic matches of actress and role in movie history! So if Emily could do that and just look straight ahead… it's cliché, but the British [say], stiff upper lip. She just had such confidence."

Shaiman certainly inherited some of that confidence, too, in composing a colossal new score for the movie. The five-time Oscar nominee's score is entirely original, save for a few honored melancholy chords of Kostal's; all in, he calls Mary Poppins Returns the biggest project of his career on every level. "Spiritually, physically, musically, lyrically, orchestrally… it's more music than I've ever written for any one movie," he says. "Three weeks of scoring. Nowadays, a movie maybe has four days. And the responsibility of it was big, and then just the logistics! It was just huge, and the orchestra was huge and big and full of virtuosic brilliant musicians."

But fortunately, Shaiman had cracked something early on in production that helped him, Wittman, and the rest of the filmmakers get through the nearly impossible task of adding a new chapter to the cherished Mary Poppins story. "At all times, the biggest emotions were of excitement like you can't even contain. A childlike excitement, and then a full terror and fear of 'How can we possibly take this on?'" says Shaiman. "I think that everyone who decided to accept the job on this movie had to deal with our own 'Oh my God,' because it's just so daunting. But you have to push that fear aside, or use it as energy. That's how I see it."

As indicative, if anything, of a key theme in Mary Poppins Returns and one of the philosophies Mary Poppins urges to those in need of a boost, be they wayward young children in need of a nanny or veteran songwriters embarking on a milestone career moment: "When the world turns upside down, sometimes the best thing is to turn right along with it."

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