Disney's "Frozen" is a bona fide phenomenon. It's become the highest-grossing animated film of all time, spawned oodles of merchandise, and is currently being spun off as theme park attractions, Broadway musicals, Disney-on-Ice spectaculars and, we're assuming, a line of high-end Olaf-flavored snow cones. The latest piece of the "Frozen" puzzle, however, is the dazzling new seven-minute short "Frozen Fever" that makes its debut attached to "Cinderella" starting this weekend.

The short is centered around Anna's birthday; Elsa, having spent so many years in seclusion, wants it to be perfect. But since she's come down with a cold, things don't go exactly as planned. (We'll keep things vague -- we don't want to spoil a second if it!) The entire "Frozen" team returns for the short, from voice talents Kristen Bell, Idina Menzel, Jonathan Groff, and Josh Gad, to songwriters Bobby and Kristen Lopez (yes, there's another insidiously infectious song to worm its way into your brain) to much of the animation team, led by returning directors Jennifer Lee and Chris Buck.

We were able to chat with Lee and Buck about where the short came from, how close it was to not getting finished, what their favorite piece of "Frozen" merchandise is, and how the "Frozen" ride at EPCOT in Walt Disney World is shaping up.

Moviefone: When did you first start thinking about this short?

Chris Buck: The idea of doing a short came up last spring. We were talking to John Lasseter about it, too, and it really seemed like a "thank you" to all of the fans. Just a short little thing like this, and we got excited about that. We were a little tired after the feature and the months after, so not until we really sat down in a room with our head story artists and started brainstorming about what it could be did we get excited. And then one of our story artists, Mark Smith, came to me and said, "What if Elsa got a cold?" And we all went, "Hmmm, okay!" We didn't get a chance to have much fun with Elsa in the feature so this was the chance. We all got really excited.

Was there any discussion about what to use in the short and what to hold back for potential sequels or follow-ups?

Jennifer Lee: No, I think, obviously, this is coming from us and Bobby and Kristen Lopez too, we know the "Frozen" characters very well, we know what they would and wouldn't do, we know the choices they would make and things we don't want to happen and we obviously stay true to that. But the bigger thing was just making sure we were creatively open and saying "What if?" and shaking things up a bit. We had to get everything that happened with "Frozen" out of our heads just so we could think, What would Anna do? What would Elsa do? And staying true to them and exploring things like how Elsa and Kristoff had never talked to each other in the feature so that would be nice to see, so we did. But being that short and being that it takes place in one day, it wouldn't take away from the fun people were having about where these characters were going next.

Can you talk about developing the look of "Frozen Fever"? It's kind of fun to see the kingdom with a springier color scheme.

Buck: We got a lot of our team back together to do the film, so our art director was back and we gave it that "Frozen" look. He's great with color and design so we wanted to stay true to the original and Arendelle. So it's pretty much Arendelle set in the summertime and how beautiful that could be. That was it. Instead of the wintery color scheme from the movie we got to play with more summery stuff.

What was it like working with the Lopezes again? They're obviously a huge part of the make-up of the franchise's success.

Lee: Well, what's nice is that we worked very, very intensely with them for a good 14 to 15 months and shaped the story with them, so we had a shorthand throwing out story ideas and giving them the broad strokes of where we were going and supporting that with visual gags and things. And they find the hook -- that song that they can write that resonates. We hit a nice balance, since the song is quite sincere and it's the emotion of the film; it's the girls, it's their relationship, and the visuals support it with playfulness. And that's what we've done a lot with them. It was a bit of a groove that we came to know, which was very helpful. But we also couldn't imagine doing it without them. They know these characters as well as we do.

How difficult was it to get this short done on time?

Buck: It was tight. We started working on it last June. That was just coming up with the idea. And production-wise, we had to squeeze in at the end of "Big Hero 6," before the animators started in on the next one. Everybody wanted to work on it. A lot of the animators had such a good time on the first one that they came to us and said, "Can I just do one scene?" And even our head animator on Olaf came back and did one scene.

Lee: So we have a lot of animators on this because everyone said, "Can I just do one?" That meant a lot to us -- that people wanted to come back. The concern in the beginning was always, Will it be good enough? Will it do it justice? Do you have the creative energy to do it? So we couldn't put it into production until we had found it. So the summer was pretty intense in terms of getting it right or getting it to where it could go with animation. The song came about pretty quickly, which helped. But we were recording voices in August and we had just sat down with it in June. But we tend to work that way -- really intense, really fast.

This movie has clearly taken on a life of its own. What is your favorite bit of "Frozen"-related merchandise?

Lee: Ooooo...

Buck: Uhhhh...

Lee: Could it be good or bad? My mind is now spinning.

Buck: For the bad, the bad would be that there was a Halloween costume for women... It was Olaf...

Lee: Sexy Olaf.

Buck: That would probably be my favorite bad one. I don't think it was Disney sanctioned. It was pretty impressive though.

Lee: For good I think to the thing that inspired a lot of eBay price fights, which were the dresses. Because when I was growing up as a girl, they didn't have these. They didn't have the Disney Princess dresses. And I was obsessed with "Cinderella" and making dresses out of my mom's slips and things.

Buck: You said the mice were helping you with that!

Lee: So particularly Elsa's dress, every time I saw a little girl in that, I could just feel how they were feeling and how much they were enjoying throwing their arms out and pretending to make snow. That doesn't get old.

"Frozen" will be a franchise that will go on for many years. How do you delegate shepherding the "Frozen" brand with working on other projects of your own?

Lee: I'll let you know once we figure out how to do it right. It's a challenge, and it's a good challenge to have. We can be quite tired, but I would say that's a champagne problem to have this amount of support creatively from Disney on all fronts -- the musical, the "Wrinkle in Time" animation, the parks; just the fact that they want us from us keeps us going, even when we're tired.

Buck: What's great too is that they've actually asked us to hop on these things. Sometimes in the past, once you finish the film, you hand it over and that was it. That was the last time you had any input that came after the film, so it's nice that we're asked and are able to tell them what worked, what didn't work, and give them some advice in keeping them true. It helps to keep the integrity of these characters and this property.

You brought up the parks. What's the status of the Norway ride at EPCOT and how's it coming along?

Buck: I'm not sure of the date, I think spring of next year. It's looking very, very good. We've been in on the early designing and I'm excited by the look of it.

Lee: Chris has been working with them daily, and I of course threw up when they showed us the 3D version in the simulator. So I'm not going anywhere near it.

Buck: It's going to have real state-of-the-art audio animatoronics and it's going to look amazing.

What has it been like seeing the characters embraced at the parks?

Buck: Oh, it's crazy. Especially when you see the response with the meet-and-greet characters. I was walking by the meet-and-greet at Disneyland last summer, when the lines were extremely long, and I was with someone and they said, "You should tell them you're the director." And it's like this four-hour line of parents and kids, and I said, "I'm not going to tell anyone I had anything to do with it."
Elsa celebrates Anna's birthday by throwing a party full of surprises and presents, including summer dresses, until Elsa's icy powers have a few unintended consequences. The all-new Walt Disney Animation Studios short