Google the story - using images (or even use something like "cat hat birthday cake")
Get some marzipan from the store
Copy the chosen image. Copying is a lot easier and since you'll likely make some changes, and you're not selling it, you have "fair use - one time, academic" privilege. You're learning how to make the marzipan, ergo academic.
It's not hard. I used to copy the pictures out of the Cakeworks magazines to make birthday cakes for my kids.
Linda in northeast Iowa