I've been successful w/ adding PB to a box mix, but I love the Hershey's chocolate cake! And I was wondering if I could add PB to it? I'm not all smart w/ the science of scratch baking so I didn't know if I would need to add or eliminate any ingredients from the recipe or just add it to the batter. Any suggestions on how much?

Thanks in advance

Here is the link to the recipe

http://www.hersheys.com/recipes/recipes/detail.asp?id=184&page=1&per=25&keyword=chocolate%20cake#content_area