For the new movie "Blue Moon," starring Ethan Hawke as the famed Broadway lyricist Lorenz Hart, a replica of the iconic West 44th Street theater restaurant Sardi's was built in a Dublin, Ireland, film studio -- 3,000 miles away.

"We have to build Sardi's somewhere," director Richard Linklater told The Post. "They're not going to give us Sardi's for a month."

Ultimately the crew jetted to the Emerald Isle.

"The historical challenge is very real," Linklater added. "We redo all those pictures. You read every book. You get the actual designs, the architectural drawings. So it's fun to do a very, very specific recreation."

Of course, structural changes were made to suit the unique needs of the film, which is set on March 9, 1943, the opening night of Rodgers and Hammerstein's "Oklahoma!"

The downstairs bar, where most of the witty action takes place while whisky flows, is much smaller in real life.

Hawke's Hart, Bobby Cannavale's bartender and Andrew Scott's Richard Rodgers, who wrote "Pal Joey" and other shows with Hart before partnering with Oscar Hammerstein, needed room to spread out.

And there are easter eggs hidden in the newly created celeb caricatures hanging on the wall.

But the classic style and ambiance of the New York institution, which first opened in its current location in 1927, are spot on.

Remarkably so, because Dublin-based production designer Susie Cullen has never step foot in Sardi's before.

"I was sent videos of a walk-through," Cullen told The Post. "As you walk in through the door and what you see when you look left, what you see when you look right."

She added: "We changed reality and made it work."

Cullen prioritized what she believed were the eatery's important aspects: the amount of cartoons on display, the deep red and brown color tones and the abundance of dark-stained wood.

The film was made on a tight budget. So, the designer borrowed flats from other projects.

And some 100 original caricatures were drawn by a local artist to look like the well-known portraits at Sardi's.

But they're not all of Broadway royalty of the day like Tallulah Bankhead and Ethel Barrymore.

"A few crew members appear amongst the characters," Cullen said. "Like Richard [Linklater] is in. John Sloss, the producer, and his family, and one of the other producers, a couple of art directors."

Another aspect of creating Sardi's of-a-different-era atmosphere is the performances. Hawke and Cannavale did hands-on research to nail the vibe.

"Ethan and I live three blocks away from each other," Cannavale told The Post.

"So, like the month before we went to Dublin, we went to Sardi's a few times and we hung out. And we've hung out there before because we've had opening night parties there. And I think we both have our caricatures up on the wall."

Then, on the night prior to flying to Dublin, Hawke told The Post, Tony winner Patti LuPone walked in and joined the pair for a drink.

"Patti LuPone was holding court and people were coming in, and there was all kinds of Broadway gossip happening," he said.

"And Bobby went behind the bar and, you know, asked the bartenders about different details about what it's like to work there and how it would have changed."

Actually, making "Blue Moon," which is now in theaters, proved something of a homecoming for Cannavale, who currently stars in "Art" on Broadway with James Corden and Neil Patrick Harris.

"I worked in a lot of bars in New York City," he said. "Not Sardi's, but yeah it did feel pretty authentic to the actual Sardi's for sure."

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