After a hot minute away from Instagram last year, Hailee Steinfeld dropped a beauty bombshell: She joined Team Bob. The actor, known then for her extra-long, undulating lengths, posted a snap of her chin-skimming new haircut.

Hairstylist and RŌZ haircare founder Mara Roszak had crafted Steinfeld’s bob just as she began filming for her—now, newly released—horror movie Sinners. And she’s just shared dropped some BTS on how she made it happen way back when Steinfeld sat in Roszak’s chair with almost waist-length hair. “Hailee has always been a long-haired girl and this was a really big chop and change,” Roszak tells Vogue. “I was honored to be asked to do it. We wanted it to work with the film period film, but also work with Hailee’s off days.”

Photo: Instagram (@mararoszak)

Sinners is the historical supernatural horror film set in the 1930s in Mississippi (feat. some vampires), and sees Steinfeld star as an (undead) woman of the south. Her hair, then, reflected the era’s aesthetics. “We did a ‘S’ wave shape which shortens the style by one to two inches,” explains Roszak. “We wanted to leave a little length to account for that. We trimmed subtle layers around Hailee’s face, and cut the hair just above the collarbone.”

References for the look included one of cinema’s golden age actors—The Big Sleep’s Lauren Bacall, who had a signature, coiffed and wavy, clavicle-touching long bob. As well, images of sophisticated women of the ’30s, that recall a more “classic and conservative” look. “We’re calling it a ‘swing bob,’” says Roszak.