Pianist and piano professor Julian Jacobson continues his Beethoven marathon series. Beethoven’s monumental Sonata in B flat major Op. 106, known as the ‘Hammerklavier’, is today’s chosen topic. Ah, the redoubtable Hammerklavier. Beethoven’s “ne plus ultra” piano work, unless it be the Diabelli Variations. The piece that was regarded as unplayable, a closed book, until…