Pi in the Sky by Wendy Mass
"Joss is the seventh son of the Supreme Overlord of the Universe. His older brothers help his dad rule the cosmos, but all Joss gets to do is deliver pies. That's right: pies. Of course, these pies actually hold the secrets of the universe between their buttery crusts, but they're still pies.
Joss is happy to let his older brothers shine. He has plenty to keep his hands full: attempting to improve his bowling score; listening to his best friend, Kal, try (and fail) to play the drums; and exploring his ever-changing home, The Realms. But when Earth suddenly disappears, Joss is tasked with the seemingly impossible job of bringing it back. With the help of Annika, an outspoken girl from Earth, he embarks on the adventure of a lifetime...and learns that the universe is an even stranger place than he'd imagined."- summary from Amazon
I love Wendy Mass' books so much; they're so clever and well-written. If you haven't read a book by her, go read one. It doesn't matter which because they're all amazing. They're very smart middle-grade books and this one is no exception. It's all about the universe and building one, so there are some scientific aspects to it (some of which flew over my head, lol) but it's very much from a kid's perspective. Joss and Annika are great characters and I loved seeing them interact with each other and work together on this crazy journey; there's some good humor and a little flirting between the two of them as they get to know each other. It's all very sweet.
Overall, just another wonderful, original book from Mass. Again, if you haven't read anything by her yet, get on it!
FTC: Borrowed hardcover from library. Link above is an Amazon Associate link; any profit goes toward funding contests.