I like the idea Belle may have written the book. It might also explain the Belle in the padded room being tormented by knowing the truth. Perhaps, the Evil Queen/Regina locked her away in a tower until she had compiled a book of every story in the land and could recite them by heart. As a component of the Dark Curse, all these stories were entombed inside Belle’s broken heart thus why her counterpart in Storybrooke is really Belle gone mad 1000 times more than Jefferson, who only has to remember the two lives in his own head. Imagine, the insanity that could be caused by all those lives screaming to get out. That’s a serious case of Multiple Personalties Disorder, there.
However, in the latest episode (An Apple…) Jefferson is bargaining with Regina about his daughter, Grace, and says he’ll do as Regina wishes if she will “write a new story for Grace and I” instead of just waking her up to live with two worlds in her head like he has had to. That line of dialogue made me think Regina had something to do with the story book – or – has some other book that is something like the false reality the Curse reads from to veil the minds of the Storybrooke citizens; an anti-Once Upon A Time book of sorts.