Saoirse Ronan’s idea of relaxing off-screen isn’t a spa day — it’s playing with sharp objects.

The 25-year-old, three-time Oscar nominee has just completed an introduction to cooking course she took with a friend in Edinburgh, shortly after wrapping production on “Little Women,” the adaptation of Louisa May Alcott’s classic novel that opens Dec. 25.

“Have you ever chopped garlic and it just gets stuck in your hands? If you run your fingernails down the safe edge of a steel knife under hot water, it comes right out,” Ronan tells Variety with an easy smile.

It’s not a huge revelation, she admits, but the actor says she needs to keep herself occupied between jobs. “I find my brain turns to mush. I go a bit thick when I’m not working, so I wanted to do something in the interim that’s not acting.”

Time off is an alien experience for the star, who is known to take big, unexpected risks on screen and has been hustling since age 12 to build the anomaly that is her résumé. Ronan’s work has almost exclusively existed in a world of small prestige dramas, gaining confidence and quality as she has grown up on movie sets around the world. There’s nary a Marvel film or action franchise under her belt, yet she remains one of the most visible and employable actors of her generation.

Her new insistence on downtime can be blamed on the breakneck pace she’s maintained, appearing in more than 10 films in the past five years — and that’s not counting a vocal turn on Adult Swim’s “Robot Chicken” and an Ed Sheeran video for “Galway Girl.” It’s an eclectic list of projects that have required her to be a shape-shifter, moving effortlessly from the shy Irish immigrant of “Brooklyn” to the Sacramento teenager with artistic ambitions in “Lady Bird” to the calculating monarch at the center of last year’s “Mary Queen of Scots.” In “Little Women,” Ronan delivers another compelling turn, portraying Jo March, an aspiring novelist who refuses to adhere to social conventions. Though prone to a mushy brain, Ronan seems certain of one thing — Jo represents the most assured performance of her career.

“It was a big step up for me as an actor,” she says. “Even with something like ‘Lady Bird,’ I was fully terrified every day. I felt, ‘I’m going to ruin this. I’m going to mess it up.’ I really felt that. It was a great experience, but I was constantly on the phone to my mom or my friends saying, ‘I can’t do it.’ It wasn’t like that with ‘Little Women.’”

The Alcott adaptation reunites Ronan with her “Lady Bird” director, Greta Gerwig. It also puts her in a cast of industry heavyweights including Meryl Streep and Laura Dern, as well as heat-seeking contemporaries such as Florence Pugh, Timothée Chalamet and Emma Watson. Gerwig agrees that Ronan seemed different on the set of “Little Women” — more poised and assured than she was during their earlier collaboration.

“Before we even started shooting [‘Lady Bird’], she was scared,” says Gerwig. “I drove her around everywhere, because she had to go to doctors’ appointments and different things to get cleared to film. She was really worried. I always knew she would be great, but she was really concerned she wouldn’t be able to find the character. With Jo, there was an extraordinary softness to her. She just knew she could do it.”

While Ronan admits she was “desperate” for the shot to play Jo, she says she was never more prepared to tackle a role. “I was ready to jump out of line and take it on. Jo is such an important figure for so many girls, and I didn’t feel daunted by it. I was precious with her,” she says.

Jo March is the lionhearted rebel at the center of Alcott’s most famous work, the story of four sisters coming of age in the Civil War era. Jo rejects the gender conventions of her time by refusing the pageantry of frilly dresses and debutante balls. She wants to be treated with the same respect as men and to be afforded the same opportunities. And yet in order to get a platform for her work she has no choice but to write pulpy short stories for newspapers under a male pen name. It’s a role that has been played by the likes of Katharine Hepburn and Winona Ryder, but Ronan is able to give the part contemporary zip. It helps that many of the issues that Alcott grappled with have a present-day resonance.

Jo’s set of values, first introduced when the book was published in 1868, have echoed throughout the decades. They have helped inform the history of feminism in this country — enabling a movie shot more than a century and a half after Alcott first set pen to paper to engage in timely conversations. Jo’s struggles mirror those of performers and creators such as Gerwig and Ronan in an era when there’s a tremendous push to achieve gender parity in the male-dominated entertainment and media space.

At the end of the new film, Gerwig invents a twist that Ronan executes to a T — a tribute to Alcott’s trailblazing spirit in which she clashes with a stuffy and chauvinistic editor (played, ably, by Tracy Letts) over the publication of her book. As Jo, Ronan demands concessions and refuses to back down. It’s an emotional moment of pride that diverges from the finish of Alcott’s novel (as well as the popular 1994 film adaptation starring Ryder) to focus not on love and marriage but on a woman who demands power in both art and commerce. Here, the stakes to be won are professional as well as personal.

In researching Alcott, Gerwig found a fascinating duality between the life she lived as a woman and the life she wrote for her fictional self, Jo.

“At the end of ‘Little Women,’ Jo gets married, has children and gives up writing,” Gerwig says. “In real life, Louisa never got married, never had children and kept the damn copyrights! She made so much money because of it. She supported her entire family, who had always been wretchedly poor. I just kept feeling — this is the thing underneath that all women have been unconsciously responding to.”

The writer-director is confident that Alcott herself never wanted to give Jo a fairy-tale fade to black, but consumers at the time were “voting with their pocketbooks,” and Alcott wanted commercial success. “I felt if I could give Louisa an ending she actually wanted for Jo 150 years later, then maybe we’ve gotten somewhere,” Gerwig says.

Amy Pascal, the film’s producer, endorsed the idea.

“Saoirse’s whole trajectory as a character is leading to that moment,” Pascal says. “We can all — women and men — see the moment to stand up for yourself and say, ‘This is mine.’ That voice whispers at you for most of your life until you can finally say it out loud.”

The idea of artists in general, and women in particular, retaining rights is not as evolved as one might think. Pascal notes the ordeal of singer-songwriter Taylor Swift, who is embroiled in a messy copyright battle with emerging mogul Scooter Braun, who purchased the back catalog that made her a star in her late teens and early 20s. Swift has shared her struggle to reclaim the songs she wrote, taking her appeals as high as The Carlyle Group, which financed Braun’s acquisition of her music. “Women owning their own work was a very new idea in 1869,” Pascal says. Pointing to the Swift conflict, she adds, “And unfortunately it’s a new idea still.”

The producer behind juggernauts like the “Spider-Man” franchise is convinced there’s an audience for a story without any explosions or extensive CGI. Pascal points to the book’s enduring popularity, noting it has never been out of circulation. But there’s no denying that “Little Women” is a risk. The film cost around $42 million to produce — not a massive amount of money, but far more than most indies — and it’s being released at Christmas, when it will do battle with the likes of “Star Wars: The Last Jedi” and “Jumanji: The Next Level.”

There are conflicting narratives on how Ronan landed her part in “Little Women.” While riding shotgun with Gerwig on the awards campaign for “Lady Bird,” Ronan says she caught wind that the Alcott adaptation was rapidly coming together at Sony with Pascal, and that Gerwig — who went from on-screen indie darling to buzzy director in one season — would now serve as helmer in addition to screenwriter.

At one rubber-chicken dinner on the campaign trail, Ronan says she “tapped Greta on the shoulder and said I heard she was doing ‘Little Women,’ and that I needed to be Jo.” Gerwig told her she had to marinate on the idea, to which Ronan patiently replied, “Oh, for f—’s sake.”

A week later, the good news hit her email inbox. She had the role.

Gerwig denies that there was any hand-wringing, saying simply that “Saoirse told me she was playing Jo.” The director accepted Ronan’s demand because, in many ways, that’s how she got the studio to give her the top job behind the camera.

“I felt the same way when I went to talk to Amy Pascal and Sony about how I had to make this film,” Gerwig says. “It was before I directed ‘Lady Bird.’ I was not at the top of anyone’s list, but I was so sure that I had to do it. I am not taken to showing up in offices and telling people they have to hire me.

It’s not something I do, and it’s not something Saoirse has ever done. I’m so lucky that she basically told me she was going to play this part.”

During a conversation with Variety, Gerwig repeatedly referred to Ronan as her “filmmaking partner,” underscoring how much of the star’s own input manifested on screen. In the film’s third act, when Jo is toiling away writing the decades-long history of her family hardships and triumphs, the character is seen in a weathered military jacket. “She said that Jo, and by extension Louisa, wrote as if they were taking over a territory,” Gerwig says. “They were expanding and occupying space like a military campaign, so she asked us to put her in a military jacket. That’s one example out of a million of what she would lead us to do.”

Ronan’s appeal for directors is her ability to transition from “factory-floor actor to movie star,” Gerwig says. “Saoirse is both, and it’s something all the great stars have. It’s an epic-ness. They hold our most outsized emotions in their person. She’s always had it, and she really lets it out to run in this movie. Through Jo, she allowed herself to be so big.”

Ronan was born in New York City’s Bronx borough (“Saoirse from the block,” her friends affectionately call her, evoking Bronx legend Jennifer Lopez’s famous anthem); her Irish parents relocated to Dublin, where she grew up, when she turned 3. Her breakthrough performance as the manipulative Briony Tallis in Joe Wright’s “Atonement” came about after the then 12-year-old Ronan submitted an audition tape shot in her living room.

“I’ve never encountered anyone so preternaturally talented in my life. It was very weird,” says Wright of the day he sat at his desk watching Ronan’s audition. “Her performance was transformative even on that little tape.”

Vanessa Redgrave played an older version of Ronan’s character in “Atonement,” and Wright recalled working with the pair on movement exercises.

“In rehearsals, I was trying to find some commonality between the two, looking for gestures that the character might have taken through her life,” he says. “I had Saoirse and Vanessa sitting in two chairs opposite each other, mirroring movements. It was a profound moment of seeing these two actresses, one at the very beginning of her career and one in the autumn of her career. I saw that line between them, and all of that incredible future laid out in front of Saoirse.”

As a preteen, Ronan did not pursue much work in the kids or family space. She has a lone young adult film among her credits (a non-starter franchise hopeful called “The Host” that was based on a book by Stephenie Meyer, author of “The Twilight” saga).

“I think I could see even then, on some subconscious level, that there was more longevity in films that had more grown-ups in them,” she says. “I was an only child who was around a lot of adults my whole life, and that becomes your safety.”

Ronan has partnered with such varied directors as Peter Jackson, Amy Heckerling, John Crawley, Wes Anderson and Ryan Gosling. She’s also worked with five women directors out of 28 completed films, an unusually high frequency given the abysmal employment numbers for women behind the camera. She doesn’t think there’s a major difference in the way they approach filmmaking.

“I’ve worked with some female directors who are quite masculine in the ways they oversee their sets,” says Ronan. “I’ve worked with some who are very quiet, and I’ve also worked with men who are really emotional and really sensitive. They all handle their authority in different ways.”

Her co-stars are another story. While working with Pugh, Eliza Scanlen and Watson as her fellow March sisters, Ronan says the dynamic was different from that of her previous gigs. On “Mary Queen of Scots,” Ronan and her ladies-in-waiting would hold lively rehearsals and exchange ideas between takes. When the men of the company arrived on set, Ronan found the women would instinctively retreat.

“We had the best boys in the world on that job, but when they would be in the room with us, we would get quiet and none of us would really speak,” says Ronan. “It wasn’t them, but that’s sort of the role you take on automatically. We need to relearn that and shake that off a bit.”

The Concord, Mass., location shoot for “Little Women” was raucous — in many ways mirroring the family dynamic of the March clan.

“We had the most energetic, emotional set,” says Ronan. “We were loud and on top of each other all the time, making dirty jokes, messing about. We supported each other and egged each other on.”

To get amped up before scenes about sibling squabbles, Pugh would ask Ronan to “slap her in the face, which I did,” Ronan says. “That’s the thing with myself and the girls, and Timmy [Chalamet], and the other young actors. We’re now growing up in a film industry where we can do that in a way I don’t think they could when other adaptations of this film were made.”

As Jo’s petulant but purposeful sister Amy, the women have the most electric dynamic in Gerwig’s script, two girls who boil over with rage as quickly as they embrace one another with urgency. Pugh says she was shocked by how normal Ronan was, knitting in between takes or preparing a traditional English Sunday roast for her costars when Chinese takeout would not deliver to the remote location shoot in Concord.

Pugh discovered “something really alive” about Ronan’s energy. “Every fight scene you see was real, and we were both in it. That’s what it’s like with Saoirse — it’s completely natural. You get to feel that way with her for a brief moment in time.”

Tom Rothman, chairman of the Sony Pictures Motion Picture Group, the studio behind “Little Women,” agrees that Ronan has entered a new acting stratosphere.

“There are a couple of scenes with Saoirse and Meryl together, and I am old enough to remember when Meryl burst on the scene at Saoirse’s age,” Rothman tells Variety. “I honestly believe that Saoirse is this generation’s Meryl. She registers on the screen with a speci­ficity and a power that very few actresses her age possess.”

It was on “Mary Queen of Scots” that Ronan felt the itch to break from the circadian rhythm of her acting process. It had become too task-oriented, too formulaic. She compares it to the cooking course she’s just taken.

“You do get to stage, as I just learned following those recipes, where I was sort of regimented,” she says. “I followed a definite set of goals. That’s the way my brain works, and I’ve done it that way for a very long time. I got to a stage where I wanted something that was a bit left of field for me.”

Ronan assumes a conspiratorial posture, glancing around the Four Seasons Hotel in Beverly Hills to make sure no one is in earshot. She confesses that she thought, in language that might make even feisty Jo March blush, “I’m going to f— with this a bit.”