Celebrities, socialites, and barons flocked to the Upper East Side's casual elegant Mortimer's restaurant, which has now been memorialised in a new coffee table book. Mary Hilliard's photographs; from Mortimer's: Moments in Time by Robin Baker Leacock, 2022; published by G Editions.

Photos show what it looked like inside Mortimer’s, New York City’s most exclusive celebrity hangout.

Before the New York eating scene was affected by the foodie movement, you could assess a restaurant by the level of its clientele, not its chef. The best people were at Mortimer’s on the Upper East Side.

“Mortimer’s: Moments in Time,” a new coffee table book by documentary filmmaker Robin Baker Leacock, restaurateur Robert Caravaggi, and photographer Mary Hilliard (available March 22 on Amazon), recalls a time when socialites, celebrities, and the city’s most powerful people mingled over cigarette smoke, bullshots, and vodka on the rocks.

Mortimer’s opened in March 1976 at 75th and Lex in a utilitarian facility that quickly became the de rigueur dining hole of the emerging Studio 54 crowd – including C.Z. Guest, Farrah Fawcett, and Iman. Glenn Bernbaum, the restaurant’s notoriously censorious and door-conscious proprietor, continued to administer the restaurant’s 19 tables like a social club for gossip columnists and their victims after the disco era ended – until his death in 1998.

Caravaggi, the restaurant’s longstanding maître d’, told The Post, “It was a bar where everybody was dressed up.” Swifty’s, Mortimer’s Upper East Side successor, launched in 1999, named after Bernbaum’s favourite pug. It currently has a location in Palm Beach, Florida, with a menu inspired by the original. “We had Frank Owens on the piano every night starting at 11:30 p.m. and going until 2 a.m. It was a gathering spot where people could also dine.”

After exchanging a box of Bernbaum’s papers with Baker Leacock, Caravaggi says he was inspired to write a book. It includes letters from Calvin Klein, Dominick Dunne, Henry Kissinger, Barbara Walters, and Irving Lazar, as well as unique menus (lunch: chicken hash, $3.95; hamburger, $1.90).

“Mortimer’s was from a period in New York that is now, regrettably, gone: the period of ‘the hangouts,'” says Mortimer’s veteran and writer Anthony Haden-Guest, referring to the old glitterati hangouts like Gino’s and Elaine’s. “It drew Eurotrash like myself, as well as a lot of Americans, and it was a terrific melting pot.”

The experience of “being there” in “the room” with “the people” is what Haden-Guest and the other contributors to the book — including writer Christina Oxenberg, Guggenheim Museum director Richard Armstrong, and late fashion icon Andre Leon Talley — recall first and foremost.

Baker Leacock, who visited the restaurant in its early days and had either the meatloaf or the chicken paillard, said, “I remember coming there for lunches and seeing [former Vogue Editor-in-Chief] Diana Vreeland at the table in the corner and seeing Anthony Quinn at another.” “It was a high-energy environment.” It was like a never-ending party. There was a sense of excitement and carefreeness that no longer exists in social life.”

However, it might be a difficult table for names that aren’t bolded (the restaurant never took reservations, officially).

Michael Gross, who contributed to the book, remembered, “Glenn certainly made me feel like an alien that first time I visited with my mother.” “He kept us standing in the entryway for so long that it was obvious no one would come over and seat us.”

Following his 40th birthday celebration, Averell Fisk (the grandson of William Averell Harriman, a railway tycoon and one-time governor of New York) recalls riding his motorbike to the restaurant to settle the bill. He was thrown out by Bernbaum because he was wearing a leather jacket.

Fisk says, “He told me I was dressed improperly.” “He never saw the cheque I had in my hand for him.” “I’m sorry, Glenn!”

Gate-crashers seeking to get a glimpse of life among the jet set or spot Liz Taylor in line for the ladies’ room were thrown out of private events, according to Caravaggi, and the 2 a.m. throng might become a bit rowdy. Richard Iselin Mortimer (no connection to Glenn), a patron and book contributor, possessed a get-out-of-jail-free card. He strolled into the restaurant one night in 1983, healthily pickled, and found it entirely deserted. So he decided to have a lark at the pub. The door had been left unlocked and he had tripped when the cops arrived.

However, not everyone got away with their misdeeds. When one of the Greek employees learned that Glenn had included him in his not insignificant will, he devised a murder plan. Caravaggi described it as “diobalical.” “I’m not sure if it was the FBI or what, but he hired a hitman, and they arrested him the day it was going to happen.”

Mortimer’s had become so associated with the lifestyle of the wealthy and greedy by the 1990s that Haden-Guest entertained Bruce Willis there as part of his research for his role in Tom Wolfe’s “The Bonfire of the Vanities” film adaptation.

Today, Haden-Guest and many of the other writers of the book bemoan the loss of the casual companionship that eateries like Mortimer’s generated.

“New York isn’t the only place where this happens. “I believe the social glue has disintegrated across the country,” he stated. “People have fallen out of touch.” It’s unusual to hear someone say, “Good morning.” If you mention that, people will be taken aback. It’s not just a case of individuals staring at their computers; it’s a complicated issue.”

But, while Mortimer’s was the right place at the right moment, Gross argues that societal hotspots still exist in uptown Manhattan’s shadows.

Gross stated, “That [original] group has gone extinct.” “It’s a whole different club now.” It’s more Jewish than WASP-y. But the Upper East Side is as well. Swells can still be found at club restaurants. But the last thing you do when you find one is tell a reporter from The New York Post about it.”