Let's now move on to the "sibling" of the Sonata in C major - Sonata in D, K. 311. Einstein begins his comments with the Sonata's 2nd movement, a charming Andante con espressione. He also makes some very interesting remarks on the innovations brought in music by Mozart, with his two Manneheim sonatas:
"How little Mozart was concerned with realism may be inferred from the fact that the slow movement of the other Mannheim sonata [K. 311] - an Andante con espressione, very childlike, very innocent - has also been taken to be the portait of the young Rose Cannabich.
This whole sonata is in a way a companion-piece to the sonata in C. Just as in the first movement of that work, the repetition of the initial motive is here avoided in the recapitulation and appears only as a surprise in the coda. In both sonatas the middle register of the instrument is cultivated in a new way; in both, the left hand no longer furnishes a mere accompaniment, but becomes a real partner in the dialogue; both works are showy. Mozart counted them among his more difficult piano sonatas - and rightly so, although even the apparently simplest clavier pieces by Mozart are difficult."
I am not sure why Mozart considered the Mannheim sonatas to be more difficult than other piano works (his late sonatas, for instance). I would personally find other pieces much harder from a technical of view. Having said that, it is very often the case with Mozart that I begin practice a piece, I realise that the notes are easy, the result comes almost at once... I think that I am now ready to perform this piece... and only then the real difficulty begins. The more one practices Mozart, the more one realises how difficult his music is.
Here is the 2nd movement (Andante con espressione) of the Sonata in D, K. 311, (Ushida on the piano).