If you want to get a sense of what former Saturday Night Live writer Paula Pell used to jot down in her journal when she was 13, dig up one of the “Spartan Cheerleaders” sketches, which Pell created with Will Ferrell and Cheri Oteri. “It was very reminiscent of the language of that journal, which is just really dramatic, but joyful,” says Pell, 52. “Joyful losers, as I call them. That optimism and that enthusiasm, even though people are booing you and giving you the finger.” To get an even better idea of what Pell was like as a youngster, you can go see Sisters, the new movie out December 18 written by Pell and starring Tina Fey and Amy Poehler. Fey and Poehler play Kate and Maura Ellis, siblings who decide to throw one last party in their childhood home before their parents sell it. Kate is the wild child single parent who's unable to get it together, while Maura is the caretaker reeling from a divorce. In one scene — when the women start cleaning out their childhood bedroom of all the mementos and junk — they read their teenage diary entries to each another. Kate’s are about sex. Maura’s are, well, more subdued. The tenor of the confessions resemble those by Pell and her own sister, whom Pell says was a "beautiful, tall '70s fox." In her own entries, Pell sounded a lot more like Maura, who writes about the grit in her rock tumbler, a subject Pell knows well. “When Amy says, 'Oh great, here’s a play-by-play of the Jerry Lewis telethon,' I used to challenge myself every year to watch the entire Jerry Lewis telethon from beginning to end, which was, like, two days long, and I used to get so off on staying up the entire time,” Pell says. “It was like I was running a marathon. I was just so proud of myself. I would make snacks and stay up all night and be like ragged in the morning. Little did I know years later I would be at SNL doing all-nighters all the time.” (You can see the cast reading from one of Pell's journals in a featurette over at Time.) Even if you don’t know her by name, Pell has probably made you laugh at some point. Sisters is the first feature she wrote herself, but she was a writer on SNL for nearly 20 years, starting her tenure in 1995. She wrote Kristen Wiig’s Suze Orman sketches and Rachel Dratch’s Debbie Downer skits. She played Pete Hornberger’s wife on 30 Rock and Ron Swanson’s mother on Parks and Recreation. She contributed jokes to Bridesmaids. Not only did the idea for Sisters spring from Pell's own journals, it’s also set in Orlando, FL, where she grew up. But Pell wasn’t just a Maura to her sister’s Kate. “The caretaking part of Maura, the being over involved in other people’s lives and problems is 100% me,” she says. “That’s 100% still my challenge in life. But I was also a big partier in high school, much more so than my sister. I was really kind of both of those girls.” In her senior year, Pell hosted an 80-girl slumber party. That night, she found one of the guests awake, drunkenly crying. The moment went in the movie, and Dratch captures the classmate's inebriated despair. "There’s always the person that’s drunk that goes down a dark road," she says. Pell used her repartee with her own sister for inspiration and also mined the interactions of Fey and Poehler, as well as her own nieces. Of course, Fey and Poehler aren’t actually sisters, but they're close enough, according to Pell. “They don’t have sisters themselves,” she says. “Our little group of ladies from SNL really created a sisterhood so that when we see each other, we pick up where we left off. It’s a very intimate sort of love, because we were always in the same comedy bunker together.” Pell has been surrounded by fabulously talented women since starting at SNL in the mid-'90s. “These women came in that were just super powers,” she says. “They were amazing, funny as hell. Molly [Shannon], Cheri [Oteri], Ana [Gasteyer], Rachel [Dratch]. They just took it by the balls.” Pell is pleased to see the comedy world become more diverse. "For many years, it was a lot of 35-year-old white guys that were in comedy." Pell herself also appears in Sisters playing Kate's ornery roommate. She started her career as a commercials actor before SNL scooped her up as a writer. It's the small parts like the one, which she makes the most of in this movie, that have always been her favorites. "Come in, get a laugh, and go — I love doing that when I can because it was my first love," she says. "What's fun now is to be able to write something that I actually perform in." By taking her talents to the big screen, she's making it pretty fun for us, too.