The story of the Boulanger sisters is tragic, touching and inspiring all in equal measure. Lili, a child-prodigy and the younger of the two, was plagued by illness throughout her short life. After her death from tuberculosis in 1918, aged just 24, her sister Nadia – the Paris Conservatoire matriarch who taught the likes of Aaron Copland, Quincy Jones and Phillip Glass – would go on to tirelessly champion her music, in doing so trailblazing the way for a generation of women conductors and composers who, without her example, may never have had the confidence to pursue careers in classical music.

Saturday night’s concert formed the triumphant conclusion to a day spent happily immersed in the work of these two women. The BBC Symphony Orchestra and Chorus under American conductor James Gaffigan provided a meaty backdrop to British tenor James Way, in a first half dedicated entirely to earlier, large-scale works by Lili Boulanger. Her Vieille prière bouddhique – which sets a French translation of an ancient Buddhist text – gave Way the perfect platform from which to showcase his silky upper-register. An undoubted Debussian influence can be heard in Boulanger’s florid orchestration and flagrant use of modal, whole-tone and octatonic melodies (a middle-section flute solo could have been copied straight out of the score to Prélude à l'aprés-midi d'un faune).

The Prix de Rome-winning Faust et Hélène, which sets a text by Eugène Adenis loosely based on Goethe’s Faust, is equally referential in style. Tenor Samuel Sakker joined mezzo Katarina Dalayman and a ferocious Benedict Nelson as Mephisto for this quasi-operatic fable, in which Faust enlists the devil to conjure his long-dead lover Hélène, only to be overwhelmed by the angry ghosts of her past lovers. Tonal centres shift endlessly; oily pianissimos build perfect tension; themes are manipulated and reworked in a manor reminiscent of Wagner’s own Faust Overture. But, despite an obvious debt to her forbears, a voice entirely her own can be discerned through cracks in both these works’ impressionistic veneers – one given free rein in her setting of Psalm 130, Du fond de l’abîme, which provided the ecstatic conclusion to the evening.

Written towards the end of her life, between 1914 and 1917, the immense drama and overwhelming sense of space that exudes from this Herculean work gives us a tantalising taste of what Boulanger might have written had she lived any longer. The opera she could have given us! Gaffigan conducted passionately, teasing out all sorts of telling details, like how Christopher Hind’s rumbling timpani conjures the depths out of which the singers’ voices “cry unto thee”. Bitonality reigns as Boulanger stacks chords on top of on another in a harmonic language almost Stravinskian in its disregard for convention: towards the work’s climax we hear an F major in the violins and woodwinds undercut dramatically by an E flat major in the cellos and basses. It drops again to a hazy G minor/C minor stack, and the progression repeats listlessly before resolving back onto F major. Unlike in Stravinsky’s Rite however, Boulanger’s polychords are for the most part subtle – subversive even. Her stacks are the pagoda to Igor’s pancake.

Of all the Boulanger works featured, only one was composed by elder sister Nadia. This was the Fantaisie variée – a piano concerto in all but name. Soloist Alexandra Dariescu did well to capture the rhapsodic grandeur of a composition that contains many elegant puzzle pieces – but which ultimately struggles to match them up in any coherent musical picture. She was the first to acknowledge that her younger sister was the greater composer (she once wrongly told Gabriel Fauré that her music was ‘worthless’). And yes, placed in conjunction with Lili’s Psalm 130, the Fantaisie variée does indeed feel ‘juvenile’, as an anonymous reviewer wrote in Le Courrier musical. But Nadia was just 25 when she wrote it, and, had she not abandoned composition so soon after, I’ve no doubt a voice every bit as enchanting as her sister would have emerged.