“We’ll see more of the book this season,” Kitsis explains. “As to who wrote the book, if that’s the real question, that’s not something we’ll get just yet.”
No one specific wrote the book.
The curse created the book — which would make sense. Regina had a fail safe for the curse, in case it was broken. The curse itself should have a fail safe for Emma, something to help Henry convince her to come to Storybrooke in order to break it.