Is it a cookie? A cake? A pie? A dessert sandwich? When it comes to the Maine whoopie pie, the answer is all of the above. In its most basic form, a whoopie pie is made up of two dark chocolate cake discs about the size of a hamburger bun with a layer of sweet, creamy, thick white frosting sandwiched between them. While the origins of the treat are up for debate, Maine claims to be the birthplace of its invention: The first whoopie pies came out of a Lewiston, Maine bakery in 1925.