Mark Shenton Meets: Waitress book writer Jessie Nelson

It takes a great baker to make a dessert pie that's both delicious and nutritious - and it takes a great writer to make a show that's as entertaining as its thoughtful. The London transfer of the Broadway hit musical Waitress, that's about to enter its third year in New York, opened at the West End's Adelphi Theatre last week to rave reviews (you can read my four-star review here).

And though there was plenty of praise for Sara Bareilles's wonderful, quirky songs and the fantastic cast that put them across so vividly, led by the brilliant Katharine McPhee in the title role, the unsung hero of the night was surely Jessie Nelson's book. Based on the late Adrienne Shelly's screenplay for her own 2007 film, it baked the right ingredients together and brought them to a simmer at exactly the right moments to bind it all together.

Meeting Nelson at her Covent Garden hotel on the day of the London opening, she insists that the main credit should belong to Shelly: "I always say Adrienne was the architect and I did the renovations. What you're doing is distilling things down - you take what she's done, knocking this wall down and plough in that direction to create something new."

Nelson began her career as an actor with an avant-garde theatre troupe called Mabou Mines when they were resident at New York's Public Theater before becoming a writer and director of films (most notably, I Am Sam, Stepmom, Corrina Corrina and The Story of Us) and television. So returning to the stage was a sort of homecoming for her.

"It's fascinating doing a musical", she says. "Often I'd write a scene and I'd think it was good - then I'd give it to Sara and it would come back as a song! That's the ultimate compliment, and you have to accept it as that. Sometimes your scene will become one line that launches the song."

The motto she lives by is: "hold on tightly, let go lightly." She amplifies: "Doing a musical is like putting a rug down - when this part curls up, you have to put that part down. You are harnessing it to keep it flowing."

Her connection to the material goes back a long way. First of all, she had a long history of waitressing herself between theatre jobs. And then, "when the movie came out, my daughter was 12 at the time, and she watched it at every slumber party we had at the house, so I must have seen it twenty times because kids watch movies over and over again. Also, Adrienne's husband had contacted a bunch of women filmmakers in LA to see if they wanted to direct any of her scripts, to keep her work alive after she passed - so I already had a relationship with her other material and her family.

"When I heard they were looking for a writer for a musical of Waitress, I thought I knew the material so intimately and could see it as a musical, even though I'd never written one. So I met with the producers, Sara and Diane [Paulus, director] and I pitched this vision I had of it. It was really musical theatre bootcamp for me, but I was a huge fan of musical theatre and I loved the form."

Four other writers had come before her - "they'd tried to crack it for a while'' - but it also proved remarkably serendipitous that the writing and lead creative team of director, choreographer and musical director turned out to be all women. "They didn't consciously set out to have an all-female team, and we didn't even know we were - we didn't clock it until we were way into previews on Broadway. And we had no idea there's never been one before us, either."

That may have been an unintentional great thing for Waitress, a story about women being told by women, though it's far from only for them: "It's a bigger theme than just male-female. It's not just about a marriage, but about reclaiming yourself in any relationship, and extricating yourself from them where you've having to diminish yourself or shrinking to fit to survive it."

The show defied the odds by having more female creatives than male ones, but it less luckily had the distinction of going up against Hamilton in the awards season: "They swept everything, as well they should! But we are also the only two shows that remain on from that season."

For Nelson, it has proved to be a dream come true to have ended up on Broadway at all. "I began my career as this experimental wild thing. But I also really couldn't bear an actor's life. I couldn't handle driving all day to auditions and waiting to be hired. I was very creative and I needed a more consistent outlet for it, so I taught myself how to write."

Her first screenplay, coincidentally, was about waitresses as well. "It was about five waitresses on New Year's Eve, and was a love letter to my experiences as a waitress. I ended up selling it to Disney, but the minute they bought it they fired me and hired several men to rewrite it and it never got made. When I directed my first feature, they asked me to go back and do it, but I'd lost trust in them.

"But I'd always been interested in these themes about waitressing and the camaraderie of the women and how close they come and waitressing as a team sport. So when Waitress came, I could pour all this into it."

Working with Bareilles, who also hadn't written a musical before, proved to be another gift. "She's heaven - so brilliant and so gifted. Neither of us knew what we doing, and that's part of why it worked out so well - we weren't aware of the rules, we just tried to write from our hearts, so there's something authentic about that process. Coming from film, as I had done, you have so many tools at your disposal, like a close-up or a cut-to. I began to realise that a song is like a close-up - you're moving more deeply into a character, and working out how you can unveil them in a deeper way."

Shelly's original character still stands tall over the project: "Even if a scene doesn't have a line of hers in it, I feel she created this character who sublimates her desires into her recipes, and that's such an original thing to begin with. I may re-write a recipe, but the idea and inspiration is hers."

And now a new London company is reinventing it anew around themselves. "Every company captures a different aspect of the show and has their own culture. This is a really beautiful company. The audience is really latching onto the humour and some of the bawdiness and the release of that."

Now she's continuing her working relationship with Bareilles, developing a new series called Little Voice together for Apple TV with JJ Abrams' company Bad Robot. "It's like Once - a piece that has a musical element in it. I think that all film people have an itch to get into theatre - there's a purity to it that is wonderful."

Waitress is booking at the Adelphi Theatre until 19th October.

Waitress tickets are available now.