Topping: Pour 1/4 cup melted butter into an ungreased 9×2 inch pie dish or round cake pan, that is about 2 inches deep. Sprinkle brown sugar evenly over butter. Dry fruit using a clean towel or paper towel. Arrange about 6-7 pineapple slices and all the cherries on top of the brown sugar. Place pan in the refrigerator while you prepare the cake batter, this will help set the topping.
Cake: Whisk the cake flour, baking powder, baking soda, and salt together in small bowl. Set aside.
Using a handheld or stand mixer fitted with a paddle or whisk 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 as needed. On high speed, beat in the egg whites until combined, then beat in the sour cream and vanilla extract. Pour the dry ingredients into the wet ingredients. Turn the mixer onto low speed and, slowly pour in the milk. Beat on low speed just until ingredients are combined. Do not over-mix. The batter will be slightly thick.
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 to prevent the top from over-browning before the center has a chance to fully cook. The cake is done when a toothpick inserted into the center of the cake comes out mostly clean.
Remove cake from the oven and cool on a wire rack for just 20 minutes. Invert the slightly cooled cake onto a cake stand or serving plate.