NORA Ephron is explaining the secrets to a successful marriage. It is ground she's been over before in her newspaper columns, blogs, novels and movies but when Ephron gives her lessons of life, you listen. Having been married three times she has also learned the hard way just what it takes to form a thriving union.

"I have several secrets," she says wryly and with a knowing smile. "One is marry a man who was unhappily married to someone else for 17 years; one is marry an Italian, that's a very good secret (the current Mr Ephron, who she has been married to for 22 years, is Goodfellas writer Nicholas Pileggi); and one is never marry a man you wouldn't want to be divorced from. Those are my three secrets of marriage."

The 68-year-old Ephron has lived quite a life, and shows no signs of wanting to slow down. She's as stylish as you might expect from a woman of her pedigree, and certainly doesn't look her age. Her book, released in 2006, I Feel Bad About My Neck: And Other Thoughts on Being a Woman has become a sort of manual for women over 50, containing witticisms such as, "Your children are gone, and they were the only people in the house who knew how to use the remote control."

The book also contains lots of tricks on how to cheat the ageing process, and Ephron seems like she's worth listening to in this regard. She looks stunning and could easily pass for 50, and is as productive as ever writing and directing movies, composing and producing plays and writing books and columns. She has that dry Jewish manner where it's hard to tell when she is being serious and when she is mocking herself and others. She twice reprimands me for bringing up things she hasn't thought about in years. I don't know if she's being serious or not. I suspect not.

Ephron's films, whether they are the ones she has written such as When Harry met Sally, Heartburn (which is based on her novel) or Silkwood, or her writer/directorial efforts such as Sleepless in Seattle, are among the most popular films of the past two decades and are all centred on love.

Her latest film, Julie and Julia, which she has written and directed, is also about love, both in the romantic sense and in terms of chronicling a deep infatuation with food. It is the tale of two cooks from different eras. One is Julia Child, the woman who taught America to recognise its beef bourguignon from its burgers. The other is Julie Powell, a disappointed and down-on-her-luck office clerk living in New York post 9/11, played by Streep's heir-in-waiting Amy Adams.

Child's story focuses on her efforts firstly to learn to cook French cuisine while living in post-war Paris with her husband Paul (Stanley Tucci) who works in the US Embassy, and then her battle to get a book of her sumptuous recipes published for the US market. This book became Julia Child's Mastering the Art of French Cuisine, a staple of almost every American home during the Sixties.

"Julia Child was a part of the life of almost everybody my age, and 10 years older and 10 years younger," Ephron explains. "It was a rite of passage if you were a college graduate in an urban environment in the 1960s. If you didn't own Julia Child there was something seriously damaged about you."

Fifty years later, amateur foodie Julie Powell decides to write a blog detailing her attempt to cook every single recipe from Mastering the Art of French Cuisine over the course of a year. The real-life blog became extremely popular not only as a chronicle of her endeavours, but also as a tale of one young woman struggling to make some importance of her life in the modern world.

If some of Ephron's previous films could be seen to be reflecting her attitude to men at various points over the course of her life, charting the ups and downs and trials and tribulations of relationships, her attitude to men in her latest movie Julie and Julia could be seen as being reflective of the stability and love in her marriage with Pileggi.

Both Julie and Julia have parallels in their lives in that they are both ably supported by the kind of loving and devoted husbands that don't often pop up on screen. "I was very lucky in that I wasn't making that up," Ephron says. "Thank God I wasn't making that up otherwise people would be probably irritated with me and say things like 'men aren't like that'. The truth is that men are like that. I happen to be married to one of them."

Ephron hasn't always been this serene about her relationships. She first married the writer Dan Greenburg when she was "25 and eleven twelfths". "I thought I was very old," she says. But how does she now view the 25-year-old Nora Ephron who was about to embark on a marriage? "I view her with sympathy. I don't know how any parent goes through their child's first wedding with a straight face. I really don't. I think almost everyone is too young to get married the first time, but I've finally figured it out."

Her second marriage -- from which she has two sons Jacob, 31, and Max, 30 -- was to Watergate journalist Carl Bernstein. It ended acrimoniously when Ephron discovered that Bernstein was having an affair while she was pregnant with their second child.

Using her mother's mantra that everything in life can be used to provide good copy, Ephron wrote the novel Heartburn, a thinly veiled account of her marriage to Bernstein with a lead character Mark who was "capable of having sex with a venetian blind".

The novel, subsequently made into a film starring Streep and Jack Nicholson, sparked outrage and Bernstein threatened to sue. She emphatically says she has no regrets about writing the book, but admits surprise at the furore which surrounded it upon release.

"I was surprised by a certain amount of it because I thought that people got awfully 'how dare she write about her marriage', which I hadn't noticed anybody saying about the thousands of men who had written about their marriages."

Born in New York in 1941, Ephron was raised with her three younger sisters (all of whom are now writers of some description) in the sunnier climes of Beverly Hills, Los Angeles. Her parents, Henry and Phoebe Ephron, were both hugely successful screenwriters, working together on some of the biggest movies of the 1950s such as Carousel, Marilyn Monroe's There's No Business Like Show Business and James Cagney's What Price Glory. In fact, the Sandra Dee character in the Jimmy Stewart film Take Her, She's Mine is based on letters the 22-year-old Nora wrote to her parents from university.

As a child of privilege in the 1950s it might have been expected that Ephron and her sisters would find themselves wealthy suitors and settle down in the housewife role. Ephron's mother, however, was ahead of her time and saw things differently. "My mother was a screenwriter so she made it completely clear to us that we were going to be something. I always thought that this was the reason why I got out of college and went to New York to become something and my three closest friends from college instead got married and then woke up several years later and went 'Oh'.

"My mother was such a rarity in that period. We were very lucky, all four of us. She just believed that if you were a woman you had a career; if you were a person you had a career, that's what she believed." To the young Ephron that career was in journalism. "From the age of 13 to about 21 all I ever thought about was that I was going to be a journalist. I wanted to be a journalist so badly my heart was bursting. Then I became one at 21 I was like, 'Now what?' It took me about a year to realise that now that I had this job I might want to try to get better at it."

The Ephron household wasn't solely a residence of forward-thinking equality. Her parents both descended into alcoholism during their declining years. As the eldest child, Nora had left for university at the all-girl Wellesley College by the time their drinking became a serious issue, but her younger sisters lived the consequences of their addiction.

"My parents were very complicated, troubled people eventually. I thought [the household] was fun and then my sisters increasingly thought it wasn't much fun because my parents became alcoholics and more and more so.

"I thought we lived in this fabulous, fun, smart house where conversation was great and everyone took you very seriously. If my parents had a couple of friends for dinner it was with all of us at the table. It wasn't like 'you have to go and eat in the kitchen because we're having grown-ups over'. There was never a sense of that."

While she may have been intent on becoming a journalist, as part of her all-round education she briefly found herself as an intern in the White House during the first year of John Fitzgerald Kennedy's two-year reign as president. Her sole regret from that time was that JFK failed to make a move on the perm-haired idealistic young woman working in his office. "I'm the only person who ever worked in the White House that he didn't make a pass at," she says dryly. "It's very humiliating, I'm sorry you mentioned it. We had a very brief relationship, to put it mildly. I thought he was one of the handsomest men I'd ever seen. The pictures do not begin to convey how attractive he was. He was just beyond handsome."

But as an idealistic young intern, was she aware of the president's womanising ways? "I knew about it, but I didn't know about it from Washington. I knew because everyone in Hollywood knew about it. My parents knew about it and they knew about several of the movie stars he'd had affairs with, so I kind of knew about it, but I wasn't one of the lucky ones."

While her regret at never having an affair with America's 35th president may be (slightly) tongue-in-cheek, I wonder is she someone who lives with regrets from her life. "You can't not regret a marriage that doesn't work," she says. "Of course you regret it. You don't regret the kids you got from the marriage, but if I could have the same kids, if that could be part of the deal, then absolutely you regret. If you don't regret things how on earth do you do them any better the next time?

"I mean, I have so many regrets." Give me one. "I wish I had bought an apartment on East-75th Street in 1971," she says. "We all think that life is like one of those Back to the Future movies and if you undo something then it would mean that everything from there on would have been different. Assuming that that isn't a rule, I have a trillion regrets. On the other hand, if that is a rule then I guess I have no regrets because I'm perfectly happy having ended up here in this room promoting this movie and travelling with my very lovely third husband."

One of the surprising elements of Julie and Julia is the physical nature of the relationship between the 50-something Julia and her husband Paul. As someone who is so vocal about her adoration for her husband (she recently claimed they have sex three times a day) I wonder how conscious an element of the film these scenes were for her.

"You don't see a lot of it. It was one of the things I loved about these two stories was that the less conventionally attractive couple was the one with the great sex life. I loved that. I knew going into the writing of the movie that I had that part of the story happening. Then, of course, Stanley and Meryl love each other so much so you totally believed the sexuality of those two people."

I suggest that it has ruffled a few people there has been several articles written on these scenes in the America press because it brings to people's minds images of their parents in bed together. She agrees, "but not in a bad way. Young people believe that their parents did it twice, or however many children they have. And people tend to believe that sex wasn't even invented until about 1985. But that's not true."

This time I think she's telling the truth.

Julie and Julia is in cinemas nationwide