When Anne Sofie von Otter steps on to the platform of the Barbican Hall this Friday night, she will be immediately revealed as a tyrant king, madly in love with a tree. She is Xerxes, historically a ridiculous and dangerous figure who ordered the waters to be whipped when his first bridge across the Hellespont collapsed in a storm.
"Of course, Xerxes is crazy, but Handel's music is gorgeous and it's a wonderful opportunity for me to sing a really big meaty role," says von Otter. And "Ombra mai fu", Xerxes's serenade to a plane tree, is, of course, the most popular piece Handel ever wrote, known in countless instrumental arrangements as "Handel's Largo".
"I would love to do Katya, Jenufa or Marie, but, alas, I cannot." So, instead of the guilt-ridden, distracted soprano heroines of Janacek or Berg, von Otter trains her mezzo voice on Handel's men. It was with the Baroque conductor Marc Minkowski that, as recently as 1997, she scored her first big Handel success in the title role in Ariodante. "I wish I'd come to Handel's operas sooner, because there are quite a few roles that would have been great when I was younger. Handel's music and tessitura, designed for the sort of big-star castrato voice of his day, suit my higher mezzo range, and those lines lie perfectly for me. Countertenor parts are too low, and I have always enjoyed coloratura."
Xerxes is coming to London from Paris, where it has just been staged. Will it feel flat having to step aside from a whole production and simply stand and deliver in a concert performance? "Not at all. I actually think it's a great way of doing opera, and thrilling for the audience. You have all the movement and the music in your body and in your brain; you know the part inside out, yet nothing gets in the way, and just the merest gesture says a great deal.
"I discovered early on that trouser roles were something I was good at. Now I've done so many of them that I know the ropes and the rest is up to the director, and listening to what the music tells you. I'm quite used to playing boys and I'm quite tired of it. The stories surrounding these travesti parts are often engrossing, but they're not real. I can't take them seriously compared with tales like Carmen, based on a woman with blood and guts. Der Rosenkavalier is beautiful and it can be done very dramatically, but it was a revelation for me to shed Octavian and get inside a gritty theatre role like Carmen."
Her interpretation of Bizet's flighty heroine at Glyndebourne last year didn't please everyone, least of all many (male) music critics who damned her age (too old), her wig (too red), her feistiness (too in- your-face), her pouting (lacking sex appeal), her archness (not voluptuous enough). "I was a bit sad that not everyone liked it, as I felt I did have something to offer. I find it strange that at one time I could get away with some pretty bad acting, and singing that was honestly not as good as it is now, yet critics took me to their hearts. Of course, every performer faces this, and it goes away towards the end of your career when everyone embraces you again. But in the meantime it does things to your self-confidence, and it doesn't make sense."
On disc, von Otter has avoided this sort of carping criticism and, indeed, any danger of typecasting. Together with Mahler, Korngold and Weill, she's recorded Berlioz, the little-known Cècile Chaminade, Schubert Lieder in rare orchestrations, and even Offenbach. She enjoys the thrill of live recording, and in the case of her most recent Handel CD, Giulio Cesare, in which she plays the intrepid soldier Sesto, it took just two concerts in Vienna and a few patching sessions to bring the disc to fruition.
"But I can also get pretty excited in a studio situation with absolutely no one there except me and the microphone. I suppose I have a sort of erotic love/hate relationship with the microphone. I know some people find that kind of artificial situation dreadful, and of course you are always encouraged by an audience if it's with you, but you can be put off if the response is chilly or distant."
It was Elvis Costello who encouraged von Otter to hold the microphone close, to achieve a more breathy, pop sound. Not in Handel, thank goodness, but in For the Stars, a CD collaboration including music by The Beatles and The Beach Boys that emerged about after she and Costello had exchanged endless notes and cassettes over two years. The word "crossover" isn't a problem, but she prefers "crosspollination".
There are disadvantages in changing genres, as she recognises. "When I first sing a different style of music, I feel like a fish out of water. It's pretty scary, a bit like starting all over again. I haven't a whisky voice, I can't belt things out, so rock isn't for me, but I am interested in the Brazilian composer Antonio Carlos Jobim, and I'm exploring folk music. I could make a good programme out of Irish, Scottish, American and Scandinavian folk songs, perhaps."
Didn't the Costello experience make her hungry to work with other contemporaries, with whom she could shape and create a piece of music? She hesitates. "If I were to commission a piece and then not like it, it would give me a bad conscience. I appreciate that new music can be exciting but it doesn't do a lot for me, frankly."
The experience of creating a role in Sven-David Sandstrom's Staden for the Royal Swedish Opera five years ago clearly hasn't encouraged her to venture further down the route of modern music but - the Swedish diplomat's daughter through and through - she's far too discreet to say so.
Her background and nationality seem to colour her personality. Rooted in Stockholm, where her husband is a theatre director and lives with their two sons, she's not attracted by the idea of moving to where taxes may be lower or the living easier. "I like the Swedish mentality: it really feels like 'me', as do the seasons and the countryside. I used to wonder why people thought I was serious, but I now realise it's do with the fact that I'm rather single-minded. I haven't time for dillydallying. It may be the way I appear, 'a serious cold Swede'." And, putting on a deep voice, she says: "Ja, jo." It's probably also a lot to do with her height, posture and direct look, which, combined with her slightly imperious air, suggest that messing with her would be futile.
Her accompanist, Bengt Forsberg, probably wouldn't accept that. Since turning pages for him in 1980, she's benefited from his vast knowledge of the repertoire and what she describes as his "bad manners". "He's very mischievous, a brilliant musician, and we travel well together on tour, enjoying good restaurants."
The perfect accompanist, then? "He used to be quite a loud piano-player, but now he understands that my voice is not like a box of hammers and strings but an extension of me, and that I may be tired or need to conserve energy in a long recital, or simply be having an off-day. We're both very opinionated and there's endless fighting, but if you go into so much detail you do have passionate discussions.
"Bengt asks me why I don't argue with other people, and how I can possibly just accept what conductors or directors say. The answer is that I don't have the energy or the will to disagree. It wears me down. So I don't stamp my foot, but maybe my grin becomes a little too fixed, my eyes grow glassy," she smiles, "in that cold Swedish way! It costs too much to fight, so I just try to understand what directors mean and have a go. If it doesn't feel OK to begin with, then maybe it will after a while. As a performer, I like collaborating. I value the insights of a good director that can bring out both the weirdest and the most wonderful things in you."
She worked briefly with the director Nicholas Hytner, and hinted that if he ever had an idea for a cross-cultural project she'd be interested. "I don't have any great ambitions to sing specific operatic parts - most of them are out of my range and grasp now - but I'd gladly do some- thing experimental, something completely 'un-Otterish'."
What excites her is something she believes would take her art forward, into the future. She's fascinated by shows such as Twentieth Century Blues, which Christoph Marthaler, the Swiss theatre director of the "meantime" (meaning "something ended, something else not yet begun"), has created around music by Berg, Coward, Mahler, Messaien and Stravinsky, among other unlikely bedfellows. "I would love it. I think that is what opera is going to look like; singing combined with theatre and dance and wonderful visual effects. It could be like the best theatre production that blows you away, totally transforms you."
'Xerxes', Barbican, London EC2 (0845 120 7550) on Friday at 7pm. Her album of Swedish songs with Bengt Forsberg, 'Watercolours', is out in January on DGReuse content