Typically, if someone went to the esteemed Aqua restaurant in San Francisco for a dish to go, they left with an order of black cod or ahi tuna tartare.

In 2006, the then-38-year-old mayor of San Francisco, Gavin Newsom, left with the number of its 19-year-old hostess, Brittanie Mountz.

The fact that Mountz was 20 years younger didn’t appear to register with the mayor at the time, with him proudly displaying her on his arm at the opening gala of the San Francisco Symphony that September.

“He makes a lot of bad choices,” an editor at a local paper, recalling the incident, told ABC. “He’s dating this girl who’s barely out of college. He lets his hormones take over.”

Or perhaps Newsom did realize that dating a teenager wasn’t becoming for a city’s top political leader, as Mountz’s age on MySpace — the hottest social media site of the time — mysteriously morphed from 19 to 26 while they were dating, the San Francisco Chronicle reported.

At the $1,600-a-head symphony gala red carpet, Newsom described his teenage date as a speechwriter, sportswriter and secretary. One of the outlets covering the event called Mountz a “youthful blonde and Keira Knightley doppelganger.”

At the time they met, Newsom had just divorced his first wife, Kimberly Guilfoyle.

Soon after the symphony coming-out, Newsom and Mountz appeared together in a San Francisco Chronicle photo montage of society bigs at a black-tie dinner dance put on by local socialite Dede Wilsey.

By the time of their next public encounter, a shopping mall opening, Newsom’s people already appeared eager to put distance between them.

When SF Gate enquired about pictures of Mountz appearing to drink from a wine glass at the opening, a spokesperson brushed it off, saying, “If she was drinking, the mayor didn’t notice,” making sure to add that they had attended the event separately. Photos of Mountz at the event were later taken down, according to a Gawker article.

In classic San Francisco fashion, local liberals seemed more irked by Mountz’s politics than the fact that she was half Newsom’s age.

When it emerged that she was a registered Republican, questions were asked. “How dare he?” a local party member fumed to ABC. “He knows how to pick ’em. You can count the young female Republicans in this town on one hand.” 

However, others felt the relationship was a more pivotal moment.

“The years after Guilfoyle, [Newsom] was a little checked out; he was more absent in City Hall than many San Francisco mayors are,” Chris Daly, a member of the San Francisco Board of Supervisors from 2001 until 2011, told The Post.

Speaking of Newsom’s time with Mountz, Daly — whose views were often left of Newsom’s — said, “It was a gotcha moment.”

He felt it was important enough to produce an opposition ad mimicking the event, using sock puppets, portraying them as “looking down from their castle at the needy rabble below.”

Newsom, now 58, was anointed through California’s political ranks, going from mayor to lieutenant governor in 2011, then becoming governor in 2019, a term which will end in January 2027.

However, it is only now he notes, in his new memoir “Young Man in a Hurry,” “I thought of myself as a single guy who happened to be mayor. Had my head been on straight I would have seen it the other way around.”

He certainly seemed to be in a hurry to forget Mountz, as she doesn’t make the pages of the upcoming book. A spokesperson for Newsom’s office tried to play down their relationship as a mere “friendship.”

Newsom also brushed it off, telling the Times they only “went on a few dates.”

Mountz did not return a request for comment, but now works under a different name as a therapist, specializing in, among other things, “men’s issues.”

On a biographical page for her services, she writes: “I came into the field when I was 19 years old” — right around her time with Newsom — “during undergrad, and have been committed to relational healing work ever since.”

Congressman Kevin Kiley (R-Calif.), who has spoken out against Newsom, views his omission of the relationship from his story as a lack of transparency.

“It does not come as any surprise that the governor would try to create a self-serving narrative on any topic that is fully at odds with reality,” Kiley told The Post.

“He’s demonstrated an extraordinary capacity for delusion and denial.”

In his book, Newsom admits to other lapses of judgement, including his affair with Ruby Rippey Gibney, his appointments secretary as mayor. She was married to his campaign manager and good friend, Alex Tourk, at the time. Newsom admitted the affair in 2007, after Tourk resigned.

Newsom, who had a “squeaky-clean image” in the early aughts, also writes about his relationship with Sofia Milos, claiming he ditched the “Sopranos” and “CSI: Miami” actress on the advice of a pal, oil magnate Gordon Getty.

Milos told The Post: “We chose to part ways and have since moved on with our lives.”

Newsom also quickly moved on from Mountz, being set up with filmmaker Jennifer Siebel — who would become his second wife — on a blind date in October 2006.

But it wasn’t their final encounter. Mountz got a job as a reporter for a local publication, Benefit, and ended up covering the red carpet of a Will Smith movie, “The Pursuit of Happyness,” on December 8, 2006, which Newsom and Seibel attended.

Upon spotting Mountz, Newsom gave her shoulder a pat and kissed her cheek, according to a local report. He then headed off into the theater, leaving her on the other side of the velvet rope that divides the public and press from the privileged VIPs and stars.