1.Pour 1/4 cup melted butter into an ungreased 9-inch pie dish. Sprinkle brown sugar evenly over butter. Blot any excess liquid off the fruit with a paper towel. Arrange 7 pineapple slices and all the cherries on top of the brown sugar. Halve 3 pineapple rings and arrange them around the sides of the pan, too. Place pan in the refrigerator.
2.Preheat oven to 350°F. In a small bowl whisk the cake flour, baking powder, baking soda, and salt together. Set aside.
3.Using a stand mixer fitted with a paddle attachment, beat the butter on high speed until smooth and creamy, about 1 minute. Add the sugar and beat on high speed until creamed together, about 1 minute. Scrape down the sides and up the bottom of the bowl with a rubber spatula.
4.On high speed, beat in the egg whites until combined, then beat in the sour cream and vanilla extract. Scrape down the sides and up the bottom of the bowl. Pour the dry ingredients into the wet ingredients. Turn the mixer onto low speed and as the mixer runs, slowly pour in the milk. Beat on low speed just until all of the ingredients are combined. The batter will be slightly thick.
5.Remove topping from the refrigerator. Pour and spread cake batter evenly over topping. Bake for 43-48 minutes, tenting foil on top of the cake halfway through bake time.
6.The cake is done when a toothpick inserted into the center of the cake comes out mostly clean with a couple of moist crumbs. Remove cake from the oven and cool on a wire rack for 20 minutes. Invert the slightly cooled cake onto a serving plate. Some of the juices from the topping will seep over the sides. It’s best to cool the cake completely at room temperature before slicing and serving. Do not refrigerate the cake.