Memphis belle: Ginnifer Goodwin on how to dress like a film star

Designer Tom Ford has cast her in his first film and she's the 'Face of the Future' for superbrand MaxMara. As fast-rising Southern actress Ginnifer Goodwin proves, it helps to be fashion-savvy if you want to star in Hollywood

Twighlight at a mansion in the Hollywood Hills, and the moon and the starlets are coming out to play. Young actresses are arriving in their droves for a dinner honouring Mrs Nicola Maramotti, the First Lady of MaxMara (she married the founder's son). They are all studiously ignoring the cannellini and white-truffle canapés and tensing everything for photographers as they pose on the terrace against the backdrop of the darkening city sky, hung with a slender moon.

There's Mandy Moore, Rose McGowan, Tara Summers, Debra Messing – all actresses on the cusp, possibly of greatness, certainly of this sheer-drop balcony – and there, the creamiest-skinned among them (and that's creamy) is Ginnifer Goodwin, my interview quarry and the most fashion-fabulous starlet around. She's just landed a part in design mogul Tom Ford's first feature film and she's the recipient of this year's MaxMara Face of the Future Award. Hello, dimples!

Where have we seen her charmingly round cheeks before? She was Johnny Cash's first wife in Walk the Line. She was the goofy one in Mona Lisa Smile – a saccharine Hollywood version of The Prime of Miss Jean Brodie with Julia Roberts in the Maggie Smith role. Goodwin's wasn't the biggest part but she made it her own, winning laughs on lines such as "Positively vomitorious!" She has also had rave reviews for Big Love, the HBO Mormon polygamy drama in which she plays wife number three – cute, sexually insatiable and perennially pregnant – did anyone say "male fantasy"? Off-screen, she is praised for her Southern poise – she hails from Memphis – and refreshingly normal physical proportions. She talks about her "absolute resistance to getting skinny", about how important it is that women of all sizes are represented on film. She's a starlet with style and substance, which is why MaxMara has selected her for this prestigious prize – the last two winners were Emily Blunt and Maria Bello. Goodwin is going places. Unfortunately for me, literally.

She has to be up at 5am to film the third season of Big Love, so after the terrace-top photo-session, I am allowed to interview her for 12 strictly patrolled minutes. What is that, three minutes per thousand miles I've travelled to be here? Welcome to Hollywood. Another journalist, a moody Spanish correspondent, curses like a soldier when he learns how short a time we have with Ginny (her name, by the way, is the traditional Deep South version of Jennifer, pronounced with the "Gin" as in "gin and tonic").

The intimate setting for our interview: a corner of the drawing-room at the party full of starlets. She's warm and friendly with bright eyes and unnaturally shiny hair. When I ask who helped her pick out her MaxMara dress tonight, her voice is very loud, very "up!". "I worked with my stylist, Penny Lovell; we have a lot of fun." Ah, Penny Lovell – not ' quite a super-stylist like Rachel Zoe, but a former British film publicist well on her way there: she dresses Keira, you know. Her handiwork is, it has to be said, impressive – Goodwin is rocking a pair of electric-blue patent heels, incongruous with her little black dress, but in a good way. "Thank yeuw!" she beams. "They're Courtney Crawford."

Namechecking like a pro. In some ways, it's puzzling that a highly acclaimed, potentially "serious" actress such as Goodwin should choose to get so heavily into fashion. During her degree at Boston University she did three stints in England, with Lamda, Rada and the RSC; growing up she was, she tells me, "that kid who's obsessed with Judi Dench and Fiona Shaw". I hardly know whether to ask what she's reading – Madame Bovary, as it turns out – or whether leggings are over. "Whether they're in or out, they keep you warm!" She's certainly smart enough to take fashion on her own terms. "I express myself through clothes but clothes don't define me," she says firmly.

Clearly, the ladies love MaxMara – the starlets at the dinner party are all working the label enthusiastically, from Mandy Moore's classic blood-red strapless gown to Maria Bello's plunging indigo mini-dress – but I can't help wondering why it's obligatory for actresses to unite with fashion houses.

Later I put the question to Jane Bussmann, who is writing a hotly anticipated memoir of her five-year stint as a journalist in Hollywood for Macmillan (working title: The Worst Date Ever). "It's because the exposure is guaranteed," she says. "Fashion is fixed. Some films tank, some films get cancelled or put back indefinitely – but collections come out no matter what. Adverts come out no matter what. And celebs always look great in them."

Indeed, Goodwin's meteoric rise nearly stalled this autumn when her romcom He's Just Not That Into You was pushed back to early next year. It should propel her into out-and-out stardom (she has billing over Jennifers Aniston and Connelly) so waiting for its release could have been a becalmed period for her. But she was still all over Times Square in Manhattan anyway, in a Gap advert.

Getting into fashion has been a good move. It's a huge coup for her to be cast alongside Nicholas Hoult and Colin Firth in master aesthete Tom Ford's adaptation of Christopher Isherwood's novel A Single Man; even if her character, rather unpromisingly, is called Mrs Strunk, the film will surely look ravishing. But Goodwin also seems genuinely to love fashion. Cute anecdotes abound. On the set of Big Love, Chloë Sevigny gave her tips for vintage shopping in New York. Although Goodwin likes to think she dresses like an individual, "Kirsten [Dunst], Maggie [Gyllenhall] and I all have the same coat." For day-to-day dressing, she favours flats. "I only wear heels when a stylist puts me in them. My boyfriend and I like exactly where the tip of my head hits his body. Heels throw off our dynamic."

The boyfriend is American Pie actor Chris Klein, by her side tonight to see her collect her award. The two met on the set of Day Zero, and seem to be going steady. No matter that he was previously engaged to Katie Holmes (disconcertingly looky-likey with our Ginnifer, it has to be said). No matter about the old rumours that Goodwin was linked to Joaquin Phoenix during the filming of Walk the Line; even that the tears she cries on film were for their real-life relationship. She won't be drawn on any of this, except to say: "He's very considerate. Even during the scene where we had that really violent row, and he had to lash out at me, he always made sure to keep his hand under my head, so I didn't actually hurt myself."

Downstairs, on another terrace flanked by an infinity pool, the starlets are settling down to a cosy, candle-lit dinner for 50. The actress Patricia Arquette is toying with the white asparagus; Debi Mazar (GoodFellas, The Doors, Entourage) is blowing kisses to Diane English, director of her latest film, The Women. I join them nervously at the lily-strewn table. "Did you get anything good from Ginnifer?" I ask the Spanish journalist. He scoffs. "She has nothing to give me." Debi Mazar, who has a crazy-sexy-cool laugh and a sweetly adoring Italian husband, fixes me with a beady eye. "Why are you writing about all this superficial Hollywood stuff, dresses and shit? If you want to have longevity as a journalist, get into the politics of al-Qa'ida, women under the veil, that sort of thing." I notice that the infinity pool is gently steaming. It must be heated to a very high temperature.

Mrs Nicola Maramotti, tall and elegant, the perfect MaxMara ambassador, gets up to make a speech in honour of Goodwin. "We will run, not walk to cinemas to see her movie... We love the refined charm of this good Southern girl, and her timeless taste for fashion is extraordinary..." I look across the room for Goodwin, in vain. She must already have slipped away.