Fifteen years ago, Maria Ewing took Covent Garden by storm. Already an established international singer, she was making her debut there in the title role of Richard Strauss's Salome. The production was directed by Peter Hall, then her husband, and the role required Ewing to perform a Dance of the Seven Veils. Most productions find some excuse for preserving their soprano's modesty. Ewing, however, started off wearing nothing but the veils. By the end, all seven had hit the floor - and operatic Britain was at her feet as well.
She still exudes elegant, manicured glamour, but if it is opulent tales of a diva's lifestyle that you want you had better ask someone else. "Yes, you go to nice parties and people treat you well. But most of the time when I finish an opera, I come home, put on the telly or get the Hoover out. I like to be with my friends and go and have a pizza and a beer and just relax."
Home for Detroit-born Ewing is now a corner of a country estate in Sussex, surrounded by fields of sheep. And while it isn't easy to imagine this slim, collected woman munching her way through a quattro stagioni while slouching in front of Graham Norton (which, she says, is exactly what she does now and then), the vacuuming is a different matter. Her living room carpet is so dazzlingly cream you hardly dare walk on it. The furniture is Regency, narrow-legged, pale-varnished, well-loved but not exactly comfortable. Next to the white piano, however, are hearteningly messy stacks of music. Here, Strauss's Salome sits next to The Wizard of Oz, Mahler's Songs of a Wayfarer beside 50 Favourite Show Tunes. At first glance, it seems there must be two singers in the house.
But no, there's just Ewing. She is preparing the Mahler for her recital at the Wigmore Hall this Sunday, her first there for several years. Those Favourite Tunes are for less than a week later, when she will be headlining a concert of songs from MGM musicals - Singin' in the Rain, Meet Me in St Louis, you name it - at the Festival Hall in London. Extraordinarily, many of the songs, even ones as famous as Somewhere over the Rainbow, have never been heard in the concert hall in their original versions. In 1969, MGM decided it needed to make some space and threw out all the orchestral material, for even its best-loved musicals. They ended up as landfill for a California golf course. It has fallen to John Wilson, the concert's conductor, to reconstruct these orchestrations - sometimes with the help of the one surviving piano score, but more often arduously transcribing them by ear.
The idea of opera singers appropriating show tunes is anything but chic. Remember Jose Carreras on his recording of West Side Story, belting out "I saw you and the world went a-whyyyyy"? Ewing whispers the word "crossover", before discarding it. This music, she says, is as much her territory as opera. She isn't a diva being a tourist on Broadway; she is just a singer, who happens to have credentials in opera and jazz. She even notched up a couple of appearances at Ronnie Scott's last year to prove it. "One of the managers said he'd been a little nervous about booking me. But thank God he didn't say no. Then he invited me back. It was thrilling to be in that club - but I felt I belonged."
In a way, that belonging was the fulfilment of a desire Ewing had nurtured since the very beginning. "I always feel so lucky to have grown up with this music. I remember saying to my first manager in the early 1970s that I wanted to sing it, but he said I should concentrate on the classical things. And he was right - it wasn't the right time to divide the attention. But somewhere in me was this other side. So it happened in a natural way. In 1989 I was doing a concert at the Proms, and John Drummond, who ran the Proms then, asked me what I wanted to sing. And I said I'd really love to do - I don't even know how to categorise them - the great classical, popular songs. And he said, 'Right, we'll do it.'" Seven years later, another programme of Broadway numbers sung by Ewing was a highlight of the first BBC Proms in the Park event, with an audience of around 28,000.
But isn't this repertoire an easy option for a singer trained in coloratura? "Not if you're going to do it the right way. Obviously you don't have the vocal demands you have operatically. But that doesn't make it easy to sing. Often when opera singers approach this music they tend to sing in such a way that they continue to sound like an opera singer. Now, I'm not saying that's wrong, some songs lend themselves to that. But you can't do an earthy torch song with a sweet soprano-ish voice. Also, you'd be amazed at how careful you have to be vocally in approaching this music, especially the belting, throaty numbers. When it comes to singing, I don't think anything is easy."
It was at Glyndebourne that Ewing's career really began to take off. In 1978 she made her debut there in Cosi Fan Tutte, and had audiences in stitches as the headstrong Dorabella. Adding Rosina, the Composer and Poppea to her list of roles, her appearances there became almost an annual event, and in 1985 she smouldered her way through Carmen in another production created for her by Hall, who was then Glyndebourne's artistic director - and who, by this time, was her husband.
Also at Glyndebourne, she got herself a reputation for being a little difficult. Her marriage, which later broke up, began to attract more curiosity than her singing. Journalists may not be able to refer to her snippily as "Lady Hall" any more, but she still seems aware that some of that image may have stuck, and - in a soft-spoken manner - she wants to amend it. "Most people I've got on fantastically well with. But I've learned many things. I was much quicker to fly off the handle in those days. I'm not the most patient person when it comes to standards, I guess I have pretty high ones, and I care desperately about maintaining those and working hard. That's always been my priority. If I didn't like something someone did, or if a conductor was doing something I didn't understand, I would just bloody well say it. I think you have to."
Given the chance, there are roles she would like to explore yet - in Janacek's operas, for a start - and she has plans for TV projects. And she is still appearing on stage, albeit intermittently. Two seasons ago, at 50, she was singing the teenage Salome in Pittsburgh and at the prestigious Savonlinna festival in Finland. But she has fallen out of the loop with the opera houses here.
So do these two concerts represent something of a comeback? "I think that's the wrong word. I think I'm just continuing what I'm doing. I've not abandoned classical singing. If a project comes along and I'm asked to do an operatic role that is interesting and right for me dramatically and vocally - wonderful. And I'm loving doing this other music, which my heart has been calling out to for a long time. A lot of good things have happened - I don't regret any of it." Sounds like the cue for a song.
· Maria Ewing performs songs by Brahms, Mahler, Weill, Debussy and Turina at the Wigmore Hall (020-7935 2141), London W1, on Sunday. That's Entertainment - A Celebration of the MGM Musical is at the Royal Festival Hall, London SE1 (020-7960 4242), on March 22.