M ozart did it. Liszt, famously, too. You could hardly stop Bach and Messiaen – even Boulez dabbled. But at some stage improvisation disappeared from the concert platform; experimentation became something to do privately and in advance rather than in public and in real time. Unless you’re Venezuelan pianist Gabriela Montero, who has spent a career reinstating the art on the concert platform. So far Montero’s three-concert residency at the Barbican hasn’t yielded an opportunity – not so much as a cadenza – so I suspect many of the substantial audience for her solo recital were there in hopes of hearing more than just the advertised programme. They weren’t disappointed. But first there were the not-insignificant formalities of Iberia, a Spanish-themed recital that embraced 250 years of musical visitors and professional blow-ins – Chopin, Domenico Scarlatti, Liszt – alongside locals Granados, Albéniz and Mompou.…