I made a cake a couple of months ago that make a book. First I made a template of how large I needed the cover, with paper. Then I rolled out the fondant, fairly thick, about the consistency of what a real book cover would be. I then placed my template on top of the fondant and used a knife to cut the shape out. I then generously iced the cake on the side and top. Then flip the cake over so the icing is facing down and place the rectangle on the fondant. Place it carefully in place because you will not be able to lift if back up without messing things up. You then ice the other side of the cake and fold the fondant over the top. I then took white fondant and covered the exposed sides and made indents so it looked like pages. Turned out great! Everyone at the graduation party loved it!!
