The great German mezzo speaks to Tom Service about her career from budding actress to leading diva to opera director. An illuminating interview which, for once, TS didn't foul up. At one point, he lobbed up a googly by asking Fassbaender how it was that, as Octavian, she had managed so convincingly to play the part of a woman pretending to be a man dressed as a woman, trying to seduce another woman.