In April, Meryl Streep sat through a marathon retrospective of her own work during a gala tribute at the Film Society of Lincoln Center in New York City. It was a little painful to take such a long, hard look at her younger self, she admits. “They were showing clips from my earlier films. All I could see was this beautiful young woman who was anxious about whether she was too heavy or if her nose was too big. I felt like saying to her, ‘Just relax and it will all be OK.’”

It’s a surprise that this consummate actress, who always seems so calm and assured, was once riddled with insecurities. But the myth that Streep is a fantastically talented performer who never loses a moment’s beauty sleep over anything vanishes when I meet her for drinks (“Two waters, please”) at a chic hotel. She is dressed in black pants with a crocheted black top, her curtain of cornfield-yellow hair tumbling over her shoulders. Her glowing, lily-fair skin creases only when she laughs – which she does a lot. She is funny, chatty, prone to exclamations of delight as the words come spilling out. “Oh my God!” she shrieks, recalling the moment when the opportunity to play Donna in Mamma Mia! came up. “My agent said, ‘You probably won’t want to do this….’ And I was like, ‘Say yes!’” She first saw Mamma Mia! on Broadway, just after September 11. “It was a huge, immediate success because it was a reminder about where the joy of living is – singing and dancing and being in love,” she says. “I took my daughter Louisa, who was 10, and six of her friends, and we were all up dancing in the aisles.”

Streep plays a single mom with a wild past who sings ABBA songs and dances her way across a Greek island on the eve of her daughter’s wedding. The role is a departure for the serious actress who made films like Sophie’s Choice and Kramer vs. Kramer. But Streep is nothing if not versatile, seemingly capable of perfecting any accent, twanging away at country songs in A Prairie Home Companion, or crooning Ray Charles in Postcards From the Edge (listen in on youtube.com). And at 59, she is supremely aware that life should be celebrated at every opportunity. Mamma Mia! appealed to her sense of fun – and to the dreams of her youth. Raised in Summit, NJ, the eldest of three children, Streep took singing lessons hoping one day to perform opera. “My parents were very encouraging with whatever we wanted to be,” she says. “One of my brothers danced and the other had a rock-and-roll band. Not exactly the dream every father has.” Of her Mamma Mia! role, she says wistfully, “I wish my mother were alive to see this. When I was a kid, she took me to every single show. I saw the greats – Ethel Merman, Carol Channing, Georgia Brown. In high school, I was in musicals, but at college, I got diverted into acting. I never sang again for years and years.”

After graduation, Streep went backpacking in Europe. “It was the first time I’d left suburban New Jersey. I was 21. I hooked up with a woman I hardly knew and we hitchhiked.” She shudders as she lets the full horror sink in. “I’d never let my kids do that. I’d lie down on the tarmac in front of their plane.” Next month, she and her husband, the sculptor Don Gummer, who live in New York City and Connecticut, will celebrate their 30th anniversary. Their eldest child, Henry, 28, is a musician; Mamie, 25, is an actress; Grace, 22, recently graduated from Vassar College, Streep’s own alma mater; and Louisa, 17, just finished high school. Mamie and her mother costarred in last year’s film, Evening, but because they play the same character at different ages, they didn’t share any scenes. “Maybe that was for the best,” says Streep, inflecting the line with the tact, humor, and insight of wise mothers everywhere. A hands-on parent, Streep freely admits, “Lecturing is what I do with my children, not listening. Lecturing, and ordering out.”

“Motherhood, marriage, it’s a balancing act,” she continues. “Especially when you have a job that you consider rewarding. It’s a challenge but the best kind of challenge.” She has never paraded her family across the media, following a caution passed on by her Out of Africa costar. “Robert Redford taught me that when they were babies. ‘They are not your props.’ I really admired the way he protected his family. It’s something I consciously emulated.” After more than 40 films, she has never tired of the work. “In acting, living in the moment is the whole point. The trick is to live in the moment in your own life, but it’s not easy.” Still, Streep has joked that she would have preferred Mamie choose another career. “Yes, like nuclear physics!” she says, smiling. “I don’t get a choice on what Mamie does. I never have. She knows the good and bad of our business, but she loves it and she’s good.” Streep does worry about the pressures on young actresses in Hollywood to be thinner and sexier than ever. She dubs it “Victoria’s Secret syndrome” and calls it “so depressing.” For Streep herself, the last few years have provided plenty of interesting work – the dominating fashion-magazine editor in The Devil Wears Prada, a crusading TV journalist in Lions for Lambs. It was the decade before when Streep found it hard to get good parts. “I thought I was washed-up at 40. There were not a lot of interesting scripts. I could find one a year, maybe. Now I think that’s changing a little bit.” “The good thing about getting older is that when they actually do cast you it’s often something interesting,” Streep says. “Mamma Mia! is about people who are flawed and have made big mistakes, but so what?” She’s seen her peers undergo drastic plastic surgery trying to hold on to youth. “It’s not just women,” she says. “You’d be amazed at how many men in this industry have gone down that road. I just don’t get it. You have to embrace getting older. Life is precious, and when you’ve lost a lot of people, you realize each day is a gift.”

When she told her family that she was taking on Mamma Mia! the news provoked some gentle ribbing about the dance numbers’ skintight costumes. “The girls were saying, ‘Mom, please tell us you’re not going to wear spandex’ and ‘I’m going to have to move to Alaska when this comes out.’” She laughs, adding, “I’d practice singing in my closet. I’m not kidding. If it penetrated the walls I’d hear, ‘Mom. Mom. Mom!’” Filming the movie was “a joy.” In case you haven’t seen the stage musical (more than 30 million around the world have): Meryl’s character, Donna, who has brought up her daughter, Sophie, alone, is not certain who the father is. Sophie reads her mother’s diary and invites three contenders to her own wedding, hoping to uncover her dad. For Donna, it’s a collision with her wild youth; for Streep, maybe a reminder of her hitchhiker days. For her next role, Streep channels a very different muse, playing chef Julia Child in Nora Ephron’s film adaptation of the book Julie & Julia. “I’m not that great a cook. So I’m cooking my way through the Julia Child cookbook. Did you know that after cutting onions you should just wash your hands with salt?”

No doubt she’ll cook up a storm, just as she conquered disco for Mamma Mia! One of the last scenes to be shot features Donna and her girlfriends dressed, ABBA style, in silver spandex jumpsuits with towering platform boots. “It was terrifying!” Streep giggles. “I thought, Yes, this is what my daughters feared more than anything else!” When the scene wrapped, she was left with blistered feet. “I couldn’t walk because I’d been dancing in those boots all day. But I wouldn’t have missed it. It was just so much fun. And that’s got to be a good thing, don’t you think?” Hard to disagree. As the older, wiser Meryl Streep might have told her younger self, “Just relax and enjoy it all.”