Grammy-winning producer Greg Kurstin, 48, who has been behind smashes like Hello and Chandelier.
From there a partnership blossomed.
We talked together about sonically what to do with it, Kurstin recalls.

Credit: Samon Rajabnik
I immediately got a sense like, Yeah, this is going to be a really crazy album.
Its going to be really hard and then also could have some beautiful, lush harmonies.
For Kurstin, that meant pushing them at every turn musically.
I had effects and space echoes!
The sessions werent all hard work, though.
Theres an excitement and an enthusiasm like Ive never seen before.
I was really bummed when the sessions were over.
Part of that couldve been because the Foos fed Kurstin well Grohl brought his barbecue to the sessions.
That meant drawing on everything from psychedelic 60s music to angular kraut-rock to Peter Gabriel.
I would jam in the room and attempt to inspire Beck, Kurstin says.
Sias Christmas album
She is unbelievable, Kurstin says of the woman hes worked with for a decade.
I dont know how she comes up with song lyric and melody ideas so quickly.
Shes like no one else.
For her forthcoming album, that talent manifested itself as a batch of entirely new Christmas songs.
I have some sleigh bells in the studio, so I can get in the mood pretty quickly.
Working with the enigmatic singer reminded Kurstin of their early, pre-wig days together.
He seemed into the sounds I was adding, so that got me really comfortable, Kurstin explains.
I had such a great experience with him.
Though theres currently no public timetable for McCartneys follow-up to 2013sNew, Kurstin promises great things.
I feel like hes topping himself.