Upside down cakes are underutilized in my very humble opinion. This cake is super easy to throw together, and you can really get creative with the topping. I arranged it in a circular pattern, but really do you what you like. The pistachio works so well with the plums; they’re really a lovely pairing. The perfect spring dessert or summer dessert for cookouts, special occasions, Memorial Day, 4th of July, and Labor Day festivities!