Of all the foods native to St. Louis, gooey butter cake requires the least explanation to outsiders. Toasted ravioli isn't really toasted, you see, it's deep-fried. Provel, that controversial amalgamation of cheeses, has inspired more angry letters to the editor of this newspaper than any other local news issue. And ah, the sweet mysteries of the slinger and the St. Paul sandwich.... But the appeal of the gooey butter cake should be obvious from its name: Butter! Sugar! Gooeyness! Even in its purest form, gooey butter cake is irresistible. But is Marilyn Schotte, head baker at Park Avenue Coffee in Lafayette Square, content with simple buttery, sugary, gooey goodness? No, she is not. Instead, she has taken her mother's traditional recipe in 64 different directions, adding fresh fruit and candy bars and altering the batter itself to produce triple chocolate, pumpkin and white chocolate raspberry. Best of all, you can buy your gooey butter cake at Park Avenue by the slice. Why is this best, you ask? The most important thing a St. Louisan must explain to an outsider, particularly one who has just tasted this wondrous dessert for the first time and is preparing to overindulge, is that a little gooey butter cake goes a very, very, very long way.