matthew wrote:imslp wrote:Wait... is K.331 the minor key (a?) sonata? If so, then I also remember liking it a lot when I was little

I would listen to a friend of mine play it over and over...
K.331 is in A major, the third movt. (the famous "rondo alla turka") does start minor, but finishes in A major.
The minor key sonata you're thinking of is most likely to be K.310 in a minor, there's another (K.457 in c) but the a minor is the famous one.
You are most right and correct, Mozart wrote only two piano sonatas in the minor mode, and to that it should be added the fantasy in d minor, the other in c minor, not completed by Mozart but acepted as a Mozart's work, the beautiful a minor rondo and the adagio in b minor. Those are the only works in minor keys the composer wrote for piano, and they are pure god.