Writer/director/producer Judd Apatow is the prime example of "if it ain't broke, don't fix it" school of thinking. That is to say, he is renowned for working with the same actors over and over again. One of the actors whose face you will notice in the Apatow family of films is Leslie Mann. In The 40-Year-Old Virgin, she plays the drunk woman who gives Steve Carell the car ride of his life when he tries to take her home from a club, and in Knocked Up she plays Debbie, the long-suffering, long-married sister of the unintentionally pregnant Allison (Katherine Heigl). Oh yeah, and she's also Judd Apatow's wife.

"He's definitely the best director I've ever worked with," Mann says of Apatow. "He creates a really nice environment for all the actors to explore different ideas. He's very generous in that way." And while you might expect a wife to say that about her husband, Mann's statements echo not only what nearly every other living person who has worked with him will say, but also what the behind-the-scenes extras on his DVDs show for themselves.

As Mann says, the typical style of directing is "the director says action, you do the scene, and then he says cut and makes adjustments and then you do it again until he's happy." But life on Apatow's set is anything but typical, and involves a lot of improvisation from his actors to get the funniest take possible. "With Judd, he says action and then he makes adjustments while he's rolling. He rolls the film out. Then you're kind of in flow, it's not like stopping and starting ands stopping and starting," Mann explains. "It creates a fun energy and you really have to be on your toes. You really have to stay in it and be ready to do anything. He can yell out a different direction to take it in, or he can yell out different lines."

Because Apatow's movies tend to be very male-centric, Mann often finds herself the only girl in a slew of men. "I'm pretty much the girl who can hang with it," she tells me, "but there was one day when we were working on Knocked Up in the hospital scene where we're out in the waiting room. I was there with Paul and all the boys for the full day. And there was a lot of talk of porn and bongs. A lot of porn. A lot of things I haven't heard of before," she laughs. "They just laughed and laughed and thought it was the greatest thing ever."

But life was a little different most of the time on Knocked Up for Mann, because not only was her husband directing, but she was sharing screen time with her children as well. Her daughters with Apatow play her children with on-screen husband Paul Rudd. "Paul has known my kids since they were really little, so they were okay at pretending he was the dad," she says. "I didn't want to do it at first because I've seen a lot of those E! True Hollywood stories and I didn't think it was a good idea. But it turned out to be great. They've been around movie sets and they've observed how it all work. The day of shooting I was a little nervous and my daughter, Maude, was so comfortable, totally fine with two cameras on her and, like, 40 people, crew members. As calm as can be. And just like totally, really funny. They improvised like pros."

When I mention that my favorite part of the extras was watching her younger daughter, Iris, refuse to stay still during a particular scene, Mann laughs. "I haven't seen that yet. She was a little harder to get to stay put, but it worked out. She was three. She's so cute."

Mann can next be seen starring opposite Owen Wilson in the (Seth Rogen-written and Judd Apatow-produced) comedy Drillbit Taylor, which is set to open on March 21st. But in the meantime, you can catch her on the DVD of Knocked Up, which came out yesterday. Do yourself a favor and get the 2-disc edition--there's extras galore.

Click on ReelzChannel.com's Knocked Up page for clips from the movie and more!