Sounds so much like my kind of thing!
From wikipedia:
S. is a 2013 novel written by Doug Dorst and conceived by J.J. Abrams. The novel is unique in its format, presented as a story within a story. It is composed of the fictional novel Ship of Theseus by a fictional author, and hand-written notes filling the book's margins as a dialogue between two college students hoping to uncover the author's mysterious identity and the novel's secret plus loose supplementary materials tucked in between pages.