Step 1: Preheat your oven to 350°F (175°C). Grease and flour a 9-inch round baking pan or a 10-inch cast-iron skillet.
Step 2: For the topping, melt 1/2 cup (1 stick) unsalted butter in a small saucepan. Pour the melted butter evenly into the bottom of your prepared pan.
Step 3: Sprinkle 3/4 cup packed light brown sugar evenly over the melted butter.
Step 4: Arrange the drained pineapple rings over the brown sugar and butter. Place a maraschino cherry in the center of each pineapple ring and scatter any remaining cherries in the gaps.
Step 5: In a large bowl, whisk together 1 1/2 cups all-purpose flour, 1 1/2 teaspoons baking powder, and 1/2 teaspoon salt. Set aside.
Step 6: In a separate bowl, cream together 1/2 cup (1 stick) softened unsalted butter and 1 cup granulated sugar until light and fluffy, about 3-5 minutes.
Step 7: Beat in 2 large eggs, one at a time, mixing well after each addition. Stir in 1 teaspoon vanilla extract.
Step 8: Gradually add the dry ingredients to the wet ingredients, alternating with 1 cup buttermilk, beginning and ending with the dry ingredients. Mix until just combined; do not overmix.
Step 9: Carefully spoon the cake batter over the pineapple and cherries in the pan, spreading it gently and evenly to the edges.
Step 10: Bake for 40-50 minutes, or until a wooden skewer inserted into the center of the cake comes out clean.
Step 11: Let the cake cool in the pan on a wire rack for only 10 minutes. This is crucial! Any longer and the caramel might stick.
Step 12: Place a large serving plate upside down over the cake pan. Using oven mitts, carefully but confidently flip the cake over onto the plate. Remove the pan. If any pineapple or cherries stick, gently re-arrange them on the cake.
Step 13: Allow the pineapple upside down cake recipe to cool completely before slicing and serving.