As we slowly meander our way into a technology-driven era, there’s something uplifting in turning one’s thoughts to the ability of a 14-year-old boy to compose a full length opera. We are told that the origin of Mozart’s early opera La finta semplice lies in his tiger-father’s desire to impress Emperor Joseph II in Vienna, much to the general disgust of the resident Viennese composer. It was, in fact, unperformed in Vienna, the hostile forces in court and Viennese musical society putting an end to the idea of a successful performance in such inhospitable circumstances. Instead, it was given a single performance at the Archbishop’s palace in Salzburg in 1769 and has never managed to gain a large following since then. Ian Page’s unwavering commitment to the entirety of Mozart’s corpus brought his group, Classical Opera, to the Queen Elizabeth Hall for a rare semi-staging of the work.

It is, as the programme suggests, an untranslatable title, suggesting adopted simplicity, but the plot is easy enough to grasp. On an estate in Italy, the Hungarian soldiers Fracasso and Simone are billeted, overturning the quiet life of the owners, the gloomy misogynist Don Cassandro and his trembling brother Don Polidoro. Fracasso loves their sister Giacinta, and her maid Ninetta (also in love with Simone) concocts a plan to make the brothers fall in love with Fracasso’s sister Rosina who is about to begin a visit at the estate. Polidoro is completely bowled over within minutes, while Rosina’s feigned innocence beguiles and charms Cassandro. The plot wanders through the gifts of a ring, drunken scenes and duels, and a final act in which Fracasso persuades Cassandro to allow the first men who recover Giacinta and Ninetta – who have faked an absconsion with the family valuables – to marry them. Rosina drops the ignorance and agrees marriage to Cassandro, but Polidoro’s disappointment at his rejection is dispersed by his amusement at the deception.

We see in the opera much of what was to become classic Mozart; identity, class, love and forgiveness all crop up with increasing prominence in his later operas, and although the subjects were not uncommon, one can already see Mozart’s unique treatment of them evolving. The repentance scene, for example, at the end of the opera when Giacinta and Ninetta plead with Cassandro for forgiveness is right out of Figaro, the focus on intricate detail and the sheer love of tomfoolery all reminiscent of his last great operas.

Musically, although there are sparks of ingenuity, the work can be slightly wearing, even if the composer’s grip on orchestration, voice and melody is immediately astonishing. In the hands of a poor cast, it could have been frightful, but Page has a knack for assembling the ideal casts and the singers brought zing to their roles. First among equals was Regula Mühlemann, whose smooth legato, clean lines and immaculate diction gave real class to her Rosina. It’s clear she has the right voice for Mozart and her sense of fun, demonstrative enjoyment in her character’s machinations bubbled into her singing. Lukas Jakobski’s hulking, bullying Cassandro thundered around the stage in the first act, and was played so well that his superb drunken turn in the second act came as quite a surprise. Vocally, his bass is a hefty instrument with cherry-dark tones at the bottom of the voice. Alessandro Fisher’s tentative, clumsy Polidoro was equally impressive on stage; his tenor was not particularly assertive, but had a natural sensitivity to it that seemed right for the character.

Thomas Elwin gave us an earnest Fracasso, his tenor unforced and smooth with a touch of military swagger to it, while his sergeant Simone was made amiably lazy by Božidar Smiljanić, a lively bass voice with strong textures and tonal definition. Giacinta is largely left to one side by Mozart, brought out at the start and reused as a plot device in the middle, but only really coming to the fore musically in the final scene. Sophie Rennert made the best of the limited character, bringing a sense of morality and doubt to her performance and infusing the forgiveness scene with emotion. Her maid Ninetta was sung with spiky glee by Chiara Skerath.

The Mozartists gave the same high quality performance that has come to be expected from Page’s band. He is a consummate Mozartian who brings the flavours and colours of the composer to life. Among the orchestra, Pawel Siwczak’s harpsichord continuo stood out for pungency and character.