I need to make an open book cake to serve approx. 30-35 people and was wondering if I should make it out of the open book pan or two 9x13's side by side? Not sure of the serving sizes for the open book cake pan. Which way is more cost effective and will get the most servings. This cake will be covered in fondant and will have edible images on the open pages with a little girl reading a book perched on the pages modeled out of fondant/gumpaste. I think I may have under priced this cake as it is so, I want to make sure I don't under cut myself anymore. 
I think I'm leaning towards making the (2) 9x13 cakes, filled and doing a little carving. I just made a 9x13 for someone and they got 24 pieces out of it. Does anyone know how many servings I would get out of the open book pan itself? I don't have one but, will get one if it's worth it. Also, how do you fill that cake?
The wilton site claims that their book pan uses 2 boxes of mix and serves 24. Hope that helps. 
I wouldn't buy the book pan. It's pretty easy to carve an open book out of a large rectangle with very little waste, so even if you need to buy a different size rectangle than the pans you already have, at least you'll be able to use it/them again for other designs, so it's more cost-effective. A single layer 11x15 should give you 30 servings.
To carve the book, cut a V-shaped notch down the middle of the rectangle (where the "binding" of the book is). On each end (the outside edge of the "pages") you want the sides angled down. You can either just cut off the top corner all along the edge, or (if the cake isn't too small or crumbly) you can split the prism-shaped piece you just cut out of the notch in the center, flip each half over and attach to the side edges. Then for an even more realisting hardbound-book shape, cut a shallow curve into the outer half of each "page", and flip the cut out piece over so that it's on top of the inside half of each "page." The result is a flattish S-curve going from the center "binding" notch to the outside sloped side. Smooth it all out with BC before you cover with fondant.
Thank you all for your help. I will use the 11x17 pan that I have so, I don't have to buy one, YAY! and make 2 cakes to add a filling and them carve it into the book shape. I found a template on here for that. Thanks, again for all your suggestions. The cake isn't due until sept. 25th but, I will post a pic once it is done 
AI'm doing my first open book cake and my pan is 12x18x3 and have no idea how to cut it I know u have to cut a wedge in the middle but do I cut it all the way through
I made this video some time back I hope you find it useful. It does not use a book pan but two rectangular foil pans.
AThanks so can I use the pan I got and cut it in half to become two cakes
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