You worked with busbee for the first time (5 Seconds of Summer, Jason Aldean). What were you looking for in a collaborator?

Blake’s the one who said I should work with busbee, actually. [And] the thing that’s cool about him is that he has no genre boundaries. He does write for Nashville but he also does everybody else. When I went to the studio, I brought [songwriter] Justin Tranter with me because, like, what if I hated busbee? [Laughs] But we all hit it off within 10 minutes! He was like, “It needs to be raw and punk and sort of classical at the same time!”

You have classic Christmas songs like “Let It Snow” on the album, but also six original songs. Which one kicked off your writing process?

I was at Blake’s ranch in Oklahoma [this year] and there are all these exotic animals — like wildebeests! It’s like Jurassic Park. I decided to go for a run and, you know some people meditate, but I pray, so I was like “I’m going to do my physical exercise and also my mental and spiritual exercise all at the same time! So I was out there thinking to myself, “If I wrote a Christmas song, what would it be?” And, literally, this whole chorus comes out of my mouth! I was just singing out loud, by myself, with the wildebeests, this song called “Christmas Eve.” [Laughs]

Blake also recorded it for his own Christmas record. How’d he ask for that?

I’ve never had anyone record a song of mine for one of their records — let alone one of the biggest country stars ever, so I was like, “Okay, babe!” He went into Capitol Records and recorded it and then he was like, “I really think this song needs to have children on it.” So he went to the Nashville Children’s Hospital to see what kids wanted to and were well enough to sing on it. That song is like a Christmas miracle to me.

You and Blake also duet for the second time since you began dating on the title track. Did you get in the studio together? 

We haven’t directly worked in the same room. [Laughs] I’m dying to, but I’m scared! Anytime you’re going to write with somebody, it’s very intimate and it’s very scary. I’ve only recently learned how to be confident and just be like, “Why do you beat yourself up?” But he was on the bus and he was just sitting around and he came up with the “I wanna thank ya baby” melody and he’s like, “I was just sitting around and thinking about this idea and I don’t know if you can do anything with it…” He’s so humble it’s stupid. When I heard it I was like, “Oh my God, you are such a jerk! You just sent me a hit!” I couldn’t ever imagine having a better Christmas song! It’s uptempo, it’s fun, it doesn’t sound like any style, it has a country guy on it — it’s such a weird mixture! It’s almost like a No Doubt song with Blake on it.