Rautavaara may have moved away from avant-gardism in favour of mystic neo-Romanticism but the works assembled here show that he never entirely shunned serialism or related techniques, thrusting them into tonally well-behaved pieces long into his career. The composer’s single-movement Cello Sonata No 1 is carpet-bombed by fist-shaped piano clusters before it embarks on a moving process of recovery. The Cello Sonata No 2, like the First, contains examples of the brutalist symmetrical harmonies that were common in Sixties and Seventies Rautavaara.

Both pieces were started in the early Seventies but finished far later. In the First, completed in 2001, Rautavaara’s use of an almost runic melody that orbits around the middle of three adjacent notes is telling when considering his relationship to Sibelius. The Second, completed in 1991, grapples with bigger issues. It is an attractively pessimistic piece in which a remarkable central movement – a moto perpetuo on the cello beneath which broad, shadowy chords born of an entirely different velocity are laid down by the piano (again, echoes of Sibelius) – prepares the way for the angry confessions of the finale.

The neo-Baroque devices of the Solo Sonata (1969) offer Rautavaara the chance to hang melodies off a single ‘anchor’ note once more, and to explore ideas of one plane of sound restricting or controlling another (pizzicato ‘pegs’ underneath broad double-stopped lyricism, for example). This fascinating piece builds on the lessons of the Two Preludes and Fugues (1955) from the composer’s student days.

Yes, the Sonata is tricky. No, Tanja Tetzlaff doesn’t make it sound so. She can pack a punch, is always spacious, and sometimes sacrifices accuracy of tuning at the altar of expression and line. Her partner Gunilla Süssmann is absolutely in the zone, whether lowering chords into the piano with her arms in the Sonata No 2 and Song of my Heart – a refugee from the opera Aleksis Kivi – or enlivening passages including the deranged dance that is the Polska, a manic, dual-personality polka in which Tetzlaff duets with herself.