“Cha Cha Real Smooth,” at least on paper, might sound a little familiar.

The sophomore feature of filmmaker Cooper Raiff is about a 22-year-old who returns to his childhood home in suburban New Jersey the summer after graduation and develops a complicated relationship with a young mom. Ever since Benjamin Braddock coasted back to his childhood home in “The Graduate,” post-grad malaise has been an endlessly renewable resource for young filmmakers looking for inspiration.

But that wasn’t the case for ” Cha Cha Real Smooth,” which is currently available to stream on Apple TV+. The post-grad aspect wasn’t even part of the initial idea.

“The original core idea for the movie was this deep, massive, unspoken, eternal bond between a mom and her disabled daughter,” Raiff said.

Raiff has a younger sister who was born with holoprosencephaly, a condition that results in the abnormal development of the brain. In his sister Andrea’s case, her brain didn’t divide into two hemispheres. He said she can neither walk nor talk.

“My mom one time said to me something like, ‘My life will forever be defined by Andrea’s stages,'” Raiff said. “It knocked me right out. I didn’t know what to do with it other than write it down.”

He started writing some scenes but realized at some point that he was writing a relationship not a movie. So he threw a version of himself in there, the post-grad Andrew, and concocted a reason why he’d be coming into contact with this mother, Domino ( Dakota Johnson, who also produced ), and her teenage daughter, Lola. Andrew would get hired as a party-starter on the bar mitzvah circuit.

“Originally I was writing the movie about my sister. In a perfect world, honestly, I would have had her act in it,” he said.

But, he laughed, “she would have like looked into the camera the whole time.”

So, inspired by some of his sister’s school friends, he decided that Lola would have autism. And he knew it wouldn’t really come alive until they found the right actor.

In a nationwide casting search, they found Vanessa Burghardt, a New Jersey native who had been acting in local theater productions and is autistic. She’d been auditioning for “a while” but hadn’t appeared in a film. Burghardt said she tried to manage her expectations when the opportunity to audition for “Cha Cha” arrived.

“I really wanted to do well, but I’ve found that if I get too excited too early, nothing good is going to happen,” Burghardt said. “I tried to just act like I didn’t care, but I really did.”

When they saw her tape, Johnson said, “It was kind of a no-brainer… She’s so watchable and such an intelligent actor.”

Raiff said the scene she read with her mother had him in tears.

“She’s the heart of the movie,” he said. “When I saw her tape, I knew that’s what I wanted to make the movie about.”

Before they’d cast Lola, the financiers had enlisted consultants from the nonprofit RespectAbility to help guide them through working with an actor with a disability. It was something that made Raiff bristle at first, but he ended up finding it a helpful resource.

Johnson, both in her stead as a producer and Burghardt’s main acting partner, met with Burghardt on Zoom to help prepare her for what was to come.

“We went through like literally every step of what a day on set could potentially be like or what it would be like for Vanessa and timing and locations and people,” Johnson said. “(She) was like a total pro from day one. It was kind of crazy.”

The part of Lola clicked easily for Burghardt.

“I didn’t feel like I ever needed to like, like, break my brain over her,” Burghardt said. “I didn’t feel like I needed to think so much about, like, social nuances and all of those things because she was on the spectrum. I never felt like I had to question myself or my abilities to play her.”

But, Raiff is quick to remind that although both share the same disability, Burghardt is, at the end of the day, playing a character.

“I just I really, really hope to God that she gets not only plenty of auditions, but gets really taken seriously for characters that are not autistic,” Raiff said. “I know that she would knock those out of the park.”

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Follow AP Film Writer Lindsey Bahr on Twitter: www.twitter.com/ldbahr

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