Mozart’s solo keyboard music inhabits a somewhat isolated corner. Great Mozartians from Clifford Curzon to Alfred Brendel to Clara Haskil left surprisingly few recordings of the solo sonatas and variations, which is why Kristian Bezuidenhout’s mandate to record all of them on fortepiano for Harmonia Mundi catches the attention. Hearing the discs themselves, one can hardly take one’s ears off the performances because they go so far inside the music and reverse much of what you thought you knew.

Bezuidenhout seems to piggyback lesser works (variations) on to major ones (sonatas) by juxtaposing them together, paired according to similar chronology, revealing moments of synchronicity as well as dramatic leaps in Mozart’s evolution, such as on Vol 7 when the 1773 Six Variations on ‘Mio caro Adone’ in G major, K180, are followed, in 1774, by the gargantuan theme-and-variations final movement of the Piano Sonata in D major, K284, showing Mozart working with an invention and rigour that almost sound like another composer. Elsewhere, though, Mozart’s freewheeling variations, at least in these performances, are doorways into the composer’s psyche in ways that the more formal, polished sonatas are not. The variations were like Mozart’s secret garden, offering glimpses of his improvisatory spirit. Dare I say that Beethoven’s Diabelli Variations came to mind repeatedly in these three volumes?

‘When Mozart played a simple scale,’ wrote Wanda Landowska, quoting the composer’s contemporaries, ‘it became transformed into a cavatina.’ That sums up the Bezuidenhout difference. His typical Mozartian attributes include firm command of structure, great instincts for sympathetic tempi and a technique refined enough to get at the tiniest details – in contrast to Paul Badura-Skoda’s more forceful but generalised fortepiano sonorities (Gramola). More distinctively, Bezuidenhout’s elastic tempi give him room to probe for meaning but also allow panache that’s so much a part of Mozart’s buoyant temperament and prompts some delightfully elongated final cadences. Not only does one hear the notes with more transparency than on a modern instrument but one also gets a stronger sense of Mozart’s larger world. Bezuidenhout’s stealth weapon, though, may be the unequal temperament of his copy of an 1805 Anton Walter instrument. The popular notion that equal temperament reigned exclusively after JS Bach just isn’t true. Experiments with alternative tuning – I’m thinking of Peter Serkin playing late Beethoven – can be colouristic revelations, which is also true of Bezuidenhout. So if you can only afford one volume of this series, which would it be? I refuse to say. Hear them all.