Inside Idina Menzel’s unglamorous first take of ‘Into the Unknown’

Despite the majestic arc of Elsa’s “Into the Unknown,” the conditions in which Idina Menzel first rehearsed her “Frozen 2″ power ballad were remarkably unglamorous.

Songwriting duo Kristen Anderson-Lopez and Robert Lopez first heard the “Wicked” alum belt the movie’s flagship track in her dressing room backstage at an off-Broadway play. The space’s generic backdrop and unflattering lights weren’t exactly fit for an ice queen. Nevertheless, Menzel did what she does best.

“We brought a keyboard in and it was like, overhead lighting, and then she opened her mouth and sang ‘into the unknown,’ and we’re like, ‘Elsa’s back! Elsa’s back!’” Anderson-Lopez recently told The Times at the film’s red carpet premiere in L.A. “It was really magical. She turned the most mundane, drab, green-lit place into a magical world.”

The musical power couple returned to pen tunes for Disney’s highly anticipated sequel after Menzel’s “Let It Go” won original song and song written for visual media at the 2014 Oscars and 2015 Grammys, respectively. The Oscars ceremony also saw the voice actress deliver a showstopping performance of the hit, which sold millions of copies after the original film was released.

“It’s always a treat to bring a song to Idina Menzel,” Lopez said. “There’s no one like her. She has so much authenticity and emotion behind her singing, and I think that’s part of what makes her one of the best and makes her recording so iconic, is that she’s never faking it. She’s never just giving you some technical job. She’s reaching into the depths of her soul and letting that soul out.”

While “Into the Unknown” has been presented as the “Let It Go” of “Frozen 2,” the soundtrack also features several other earworms, including an eerie melody for franchise newcomer Evan Rachel Wood, who voices Elsa and Anna’s mother, Queen Iduna, in flashbacks.

“It really contains the theme of the movie and the plot of the movie coated in a lullaby,” Lopez said. “That was the first obvious moment that jumped out, like, ‘We know how to write that. Let’s do that. Let’s knock that one out.’ And it became a musical motif that Christophe Beck, the score writer, was able to weave through the film score. So we were really proud of that one.”

“Frozen 2,” starring Menzel, Wood, Kristen Bell, Jonathan Groff, Josh Gad and Sterling K. Brown, hits theaters Friday. Disney also released a pop version of “Into the Unknown” by Panic! At the Disco ahead of the film’s holiday opening.