Which female artist holds the record for the most-watched YouTube music video so far this year? Not Taylor Swift, who is on a righteous comeback trail, nor Ariana Grande, the trailblazer of 2018. It is an artist from Barcelona who trained in flamenco at the Escola Superior de Música de Catalunya, who wrote a university dissertation on a 14th-century Spanish manuscript, and is very big on nail art.

Taking the stage in Somerset House’s grand old Thames-side courtyard flanked by half a dozen female dancers, Rosalía strikes a series of poses drawn from both Iberian tradition and contemporary street dance. One particularly fierce preying mantis arm posture recurs in much of the night’s high-spec choreography. Her ruffled fuchsia top, matched with pink hot pants, visually combine proud folklore and Instagram-melting R&B couture.

Pienso En Tu Mirá, tonight’s set opener, has a few breathier passages that recall Grande, as does Rosalía’s wind-blown ponytail. But Rosalía is emphatically her own phenomenon. Not for nothing has such a mainstream outlet as Oprah Winfrey’s online magazine printed English translations of Rosalía’s most recent lyrics. This burgeoning popularity for an artist tipped since around 2017 is approaching escape velocity. Her 2018 album, El Mal Querer (loosely, Bad Loving), was rightly a sensation. It refashioned the topic of her university dissertation – La Flamenca, in which a woman is imprisoned by her jealous lover – as its central theme, modernising it with cutting-edge production and an urban sensibility.

El Mal Querer continues to provide the backbone of tonight’s electrifying set. There are hand-holds here for the casual observer getting to grips with this assured, multifaceted artist. Bagdad borrows a melody from Justin Timberlake’s Cry Me A River, while Di Mi Nombre winks at Destiny’s Child’s Say My Name, attesting to Rosalía’s grounding in classic anglophone R&B.

Just as compelling, though, is the older drama of Catalina, an update of a classic flamenco ballad by Manuel Vallejo that appeared on Rosalía’s first album, Los Ángeles (2017). She asks the crowd to be as silent as it can, for what is a masterclass in vocal control as Rosalía swells from racked coo to harsh anger.

Perhaps even better is A Ningún Hombre. Here, Rosalía’s dramatic a cappella is shadowed by a Greek chorus of backing vocals, laden with disorienting effects – far more like FKA Twigs than mainstream pop. “A ningún hombre consiento que dicte mi sentencia,” she declares – I’ll let no man sentence me.

For a mainstream-courting artist, Rosalía draws greedily from left field. Revving motorcycle-engine percussion and screeching tyres signal De Aquí No Sales (You’re Not Getting Out of Here), a series of threats of violence from a man to a woman. Soon the dancers are back, leading the fast hand-clapping – palmas – of flamenco, as the vocals themselves seem to pixelate.

Rosalía has been touring these songs for some time now – a few weeks ago, she wowed Glastonbury. But recent months have seen a concerted uptick in excitement as she has teased what everyone assumes is a forthcoming third album with a series of fiery bangers.

That most-watched video of 2019 – Rosalía’s recent collaboration with Colombian reggaetón singer J Balvin, Con Altura – came out in March. At nearly 550m views, Con Altura is, in many ways, a perfect pop storm. Sung in Spanish, the language spoken by 577 million people in the world, according to a recent study, and rising (Chinese is top of the table, English is third), it reaches parts of the world that Taylor Swift cannot. Tonight, it’s greeted with ecstatic cheers by a crowd who are in great part Spanish-speaking, but not entirely.

There’s not a lot of flamenco in Con Altura; instead, reggaetón looms large. Initially a Puerto Rican genre, reggaetón has been spreading across the Spanish-speaking world since the 90s and has been happily co-opted by US hip hop and R&B. (An old hand, Daddy Yankee – reggaetón’s pioneer – currently holds the crown for most-watched music video of 2019, male or female, with Con Calma.)

Anglophone pop artists became wise to Spanish-language trends more generally a few years back, most obviously with Justin Bieber’s reworking of Luis Fonsi’s Despacito (2017). Pop stars such as Madonna have since fallen into line. Katy Perry jumped on Daddy Yankee’s Con Calma last April with some verses. Having begun as a flamenco moderniser, Rosalía’s entry into world pop was via reggaetón. In 2018, her first massive exposure came on the back of her first collaboration with J Balvin, a guest slot on his Brillo single, reprised tonight.

Con Altura, which was her second co-sign with Balvin, is more than just the right song in the right language with the right syncopation at the right time: it’s also awesome. “Altura” is easy to grasp, whatever your mother tongue – Spanish for “height” or “altitude”, loosely, “con altura” here means “with swagger” (with the merest hint of “being high”). The video is, playfully, set on a plane. In interviews, the 25-year-old is at pains to emphasise how visuals and choreography hold equal weight to her music. Flamenco is, of course, both cante (song) and baile (dance).

In May another winning banger followed – Aute Cuture, a knowing misspelling of haute couture, again invoking loftiness. The video follows a gang of hard-as-nails manicurists; the song boasts a nagging chorus, and heaps of “altura” in the set, with Rosalía interrupting Con Altura to present a fan (the human kind) in the front row with a fan (the flamenco prop).

A week ago, Rosalía upped her game again with the double-whammy of Dios Nos Libre Del Dinero (God Free Us from Money) and Milionària, collectively released as Fucking Money Man – a rare incursion of English into Rosalía’s art. Performing it, the spotlight is on her alone, as the singer considers the root of all evil in one breath, and then, in an explosion of dancers, palmas and geyser-like vocals, plays devil’s advocate for the folding stuff moments later. There’s another outbreak of English in a captivating cover of James Blake’s Barefoot in the Park, as per the collaboration between the two artists released in April this year.

There have been questions asked in Catalonia about Rosalía’s singing Milionària in Catalan, while using Spanish expressions: the guardians of the Catalan language consider it wrong to dilute it with Spanish. A debate also rages within flamenco over Rosalía’s cultural appropriation of Gypsy traditions. But tonight’s crowd has nothing but love for this artist, whose mission is to modernise the ancient emo of flamenco and play with genre assumptions. That she does so with a knock-out voice, eye-watering imagery, wit and style is la guinda del pastel – the icing on the cake.