Montsalvatge, I guess. His Sonatine pour Yvette is a masterpiece and so are his Concierto breve and Canciones Negras. I don't know if he composed preludes. What a privilege to have studied with his daughter !
Alas no, it wasn't Xavier Montsalvatge. Of my guy I said he was better known as violinist than composer, and XM wasn't particularly a violinist, was he? I did however see archives of some of XM's articles (full of praise) writing as a critic for the Barcelona newspaper La Vanguardia
of public recitals given by various members of my guy's family, including not only my teacher but also her mother who was a pianist of some distinction. Mother and father frequently gave piano/violin recitals together.
Small hint coming up:
She (my teacher's mother, let's call her Maria, which is her real name) was a pupil of another pianist of distinction (whose name I won't reveal yet because it would be too big a hint). She (my teacher's mother's teacher) was somewhat famous, and had been his (my teacher's father's) recital partner before Maria was.