Even Schubert’s very earliest compositions terrify. His first songs, written when he was only 13, are unforgettably vivid, gory, messy, mangled, full of darkness and horror, like dead little birds. He never shakes off this Gothic sensibility; it’s never ironed out of him. A part of him remains untutored, untamed, right to the end, and over time his dark preoccupations gather a more and more frightening shape. Pitch blackness is reached in his Piano Sonata in A minor, D784, one of strangest pieces in the whole piano repertoire, a work of utter nightmarishness and a focal point for last night’s stunning all-Schubert recital from Imogen Cooper.