The Force is strong with Sandra of Socake blog. Here's how she made the Yoda birthday cake:
I wrote the birthday message on the cake board the way Yoda would speek...."30 you are" but If I had more room I would have written "Happy Birthday you must have" (I forgot to take a photo after I added the writing)
Link (with a build log, of course) - via Star Wars Blog
Hope she's as wise as Yoda... :)