Ormisda, St George's Hanover Square

The annual London Handel Festival is dutifully working its way through every one of Handel’s operas in a cycle that will eventually take us from Alcina to Xerxes before, presumably, starting all over again.

But each year, alongside these headliners, we also get a pasticcio – an opera stitched together by Handel from the shiniest and most decorative musical scraps by his European colleagues. It’s these unknown works that often throw up the biggest surprises, giving us a wide-shot of a broader musical landscape now all but obliterated by Handel’s popularity.

The term "pasticcio" originally meant pie or pastry, and like its namesake a good operatic pasticcio requires plenty of musical meat. Ormisda positively overflows with it; melodically it’s one of the most generous of all the works Handel assembled, and the combination of arias by Hasse, Vinci, Leo, Orlandini and Giacomelli was such a hit with audiences of the 1730 season that it received a massive 14 performances. (To put that in context, Giulio Cesare ran for just 13 nights.)

Nearly 300 years later it’s still a winning formula, especially when performed by the ever-stylish band of Opera Settecento under Leo Duarte, and as exciting a line-up of young soloists as I’ve ever heard at the festival, including at least two recent Handel Singing Competition finalists.

It’s possible that the plot of Ormisda really isn’t all that complicated, but with no surtitles and only a grainy facsimile of the original 18^th century word-book for help, I can’t have been the only one struggling. The gist seems to be as follows: Ormisda, the Persian King, wishes to pass the rule of his kingdom to his eldest son Cosroe, and with it the hand of Artenice in marriage. But he reckons without her love for his younger son Arsace and his own scheming second wife Palmira, who both conspire against it.

The plot is, of course, only a structure on which to hang a selection of arias, and these included some real gems. Orlandini was the dark horse of the composers, contributing not only Palmira’s effortlessly graceful “Nel tuo amor” but also Ormisda’s rippling “Si, si, lasciatemi”, while Leo’s single vengeance aria for Arsace “Tuona il ciel” provided a wonderful showpiece for mezzo Maria Ostroukhova. But it’s always Hasse who dominates, proving himself every bit Handel’s equal here with Artenice’s glorious “Passaggier che in selva oscura” and Palmira’s fiery “Se qual cor”.

Maria Ostroukhova's Arsace smouldered and schemed with charisma

A finalist in the festival’s 2015 singing competition, Ostroukhova has since matured both dramatically and technically, and evolved into an assured perfomer whose dark lower register opens up into real brilliance at the top. Her Arsace smouldered and schemed with charisma, playing off the ingenuous manipulations of Ciara Hendrick’s sweetly sung Palmira. Soprano Marie Lys (another Handel Competition alumna, pictured above) grew in strength and ease as the evening progressed, spinning some lovely legatos in her two Hasse arias. Tom Verney (Cosroe) is the latest in a series of exciting young countertenors to come through the festival, making as much of this rather flaccid nice-guy role as possible, and Nicholas Mogg offered strong support as henchman Erismeno. Only John-Colyn Gyeantey’s Ormisda missed the mark a little, tending closer to Bellini than baroque in his crooning, Italianate delivery.

Bring on next year’s performance of Venceslao.

• The London Handel Festival continues until 24 April
• More classical reviews on theartsdesk

@AlexaCoghlan