From the looks of it, much of the album was recorded Chaos and Creation-style, with Paul overdubbing multiple instruments with occasional help from others. It also sounds like there are several tracks featuring unusual instruments along with recording techniques that stretch back to Paul's Beatles days, such as tape loops. You can read the entire piece here.
That started with a choir piece that Paul had worked out on the keyboard. Then we brought in David Campbell to help arrange the choir. We went into a cathedral to record that, which was really cool. It started with us in the studio. Paul had worked out some chords that he wanted the voices to do. Then we started creating different ambient noises, some of which came from tape loops. He had a little portable reel-to-reel player, the one they used on for “Tomorrow Never Knows.” That was done on this little Brenell tape machine. We created some of the sounds on that, like slowing down guitars.