Prepare the Brown Sugar Topping: Place a 9-inch cast iron skillet over medium heat. Add 6 tablespoons of butter and allow it to melt. Stir in the firmly packed brown sugar and whisk for about 2 minutes, until the sugar dissolves and the mixture becomes a bubbling syrup. Add the Vanilla: Remove the skillet from the heat and stir in ½ teaspoon vanilla extract. Mix until evenly incorporated into the buttery brown sugar syrup.
Arrange the Pineapple: Pat the drained pineapple slices thoroughly dry between several layers of paper towels. Carefully arrange the pineapple rings evenly over the brown sugar mixture in the skillet, taking care because the skillet and syrup are still hot.
Add the Cherries: Place the stemless maraschino cherries inside the pineapple rings and fill any remaining gaps with the cherries. Arrange them evenly for an attractive topping once the cake is inverted.
Preheat the Oven: Position the oven rack in the center of the oven. Preheat the oven to 375°F (191°C).
Combine the Dry Ingredients: In a medium mixing bowl, whisk together the cake flour, all-purpose flour, baking powder, baking soda, and salt until evenly combined. Set the mixture aside.
Cream the Butter and Sugar: In a large mixing bowl, use a handheld electric mixer on medium speed to beat the softened butter and sugar for about 3 minutes. Continue until the mixture looks light, fluffy, and well aerated.
Incorporate the Eggs: Add the room-temperature eggs one at a time, beating after each addition just until the yolk disappears into the butter mixture. Avoid overmixing.
Combine the Batter: With the mixer on low speed, add the flour mixture and buttermilk alternately, beginning and ending with the flour mixture. Mix just until the ingredients are combined, then stir in the 2 teaspoons of vanilla extract.
Transfer the Batter: Gently spoon the cake batter over the arranged pineapple and cherries in the skillet. Spread it evenly across the fruit, taking care not to disturb the topping arrangement.
Bake the Cake: Place the skillet in the preheated oven and bake for 35–40 minutes, until the cake is golden brown. Insert a toothpick into the center; it should come out clean when the cake is done.
Cool Briefly: Remove the skillet from the oven and place it on a wire rack. Allow the cake to cool in the skillet for only 4 minutes before turning it out.
Invert the Cake: Run a butter knife around the edge of the skillet to loosen the cake. Wearing oven mitts, carefully place a cake plate over the skillet. Keep the plate and skillet firmly pressed together, then quickly invert them so the cake releases onto the plate. Release the Skillet: Carefully lift the skillet away from the cake. If any pineapple or cherries remain stuck to the bottom of the skillet, gently reposition them on the cake.
Serve the Cake: Serve the pineapple upside down cake warm or allow it to cool to room temperature before slicing.
