“How many headbands do I have?” asked Beanie Feldstein, the star of “Booksmart,” who was standing in the elevator of a Miu Miu store in New York City recently. She was there for a fitting for the custom gown she would wear to the Oscars as a presenter, and after a pause she answered: “Easily over 50.”
She pointed out a dainty crystal-studded headband with a bow that she wore to a Miu Miu fashion show last year. At the Golden Globes, where she was nominated for her role as Molly in “Booksmart” — a comedy about two best friends in their last days of high school — she wore a shimmering navy Oscar de la Renta dress with a matching braided headband. “I love bows, color and whimsy,” Ms. Feldstein said.
Last year, she began working with Erin Walsh, a stylist whose clients include Anne Hathaway and Sarah Jessica Parker. Ms. Walsh was called in at the last minute to pull together looks for Ms. Feldstein for the movie’s premiere.
“We had never met before, but she walked in saying, ‘I was thinking … headbands,’” Ms. Feldstein said. “We have this Yiddish word for meant to be, ‘bashert,’ and it was just meant to be.”
This meeting was unusual for Ms. Feldstein, 26, who did not regularly use stylists, instead preferring to dress herself. Two years ago, she wore a dress to the Oscars that she found at Saks Fifth Avenue.
That same year, she wore her high school prom dress to the Screen Actors Guild awards, where the cast of her breakout movie, “Lady Bird,” was up for an award. Her decision was both a practical and symbolic one: “It was this sweet moment, because in ‘Lady Bird,’ my character ends the movie in her prom dress,” she said.
At the start of the fitting, Ms. Feldstein and Ms. Walsh stared at the dress on the hanger in awe and let out twin squeals of delight. After being zipped into the dress, Ms. Feldstein entered the fitting room, which was decked out in floor-to-ceiling baby blue, with Baroque-inspired wallpaper and carpet to match.
“Oh, this is just beyond,” Ms. Walsh said.
The corseted white gown, made of silk gazar and organza, was hand-embroidered with a black rose pattern and covered in sequins that make the dress look liquid when it moves. The full skirt is supported by layers of tulle and other fabrics. The dress took 190 hours to create, with 80 hours devoted to the embroidery alone.
Sophia Loren was the inspiration for the look, Ms. Walsh said, pointing out the square halter neck of the dress. “We wanted old Hollywood glamour,” she said. “Something incredibly sensual, powerful, feminine and whimsical to create this movie star kind of moment, and the color and fabrics were influenced by that.”
Ms. Feldstein’s voice filled the room when she spoke, clear and excited. “It’s not in charge of me, I’m in charge of it,” she said, laughing as she walked in a circle around the room after being pinned and prodded for fit adjustments.
“It makes her look like a beam of light,” Ms. Walsh said.
Ms. Feldstein hopped from side to side, angling her face as she tested the weight of the dress. “It’s heavy, but my dress in ‘Hello, Dolly!’ was 20 pounds and we did a whole polka in it,” she said, referring to her Broadway debut in 2017. “Trust me, I’ll be O.K.”
Soon came the ultimate test: Could she sit in it? Ms. Feldstein perched on a chair, her skirts billowing around her.
“Good luck to my mom sitting next to me,” she said of her mother, who is her date at the ceremony. “She’ll be using it as a blanket.”
Ms. Walsh plucked a velvet black crystal-embellished clutch off a nearby table and handed it to Ms. Feldstein to finish the outfit. “Look, you can actually fit stuff in it,” she said.
“What a dream,” Ms. Feldstein said. “My inhaler will have ample room.”
