In a large, 9-inch skillet, melt butter in the oven while it’s preheating. Remove from oven and stir in brown sugar; mix until well combined. Line the bottom of the skillet with pineapple slices.
Beat egg whites on medium-high speed, slowly adding sugar until medium stiff peaks form.
In a separate bowl, beat egg yolks until light and fluffy. Add flour and baking powder and mix until combine. Gently fold in egg-whites, turning the batter over and over with a spatula.
Once batter is well mixed, pour batter in the skillet. Bake at 350° F 30-35 minutes until lightly golden brown on top. Test the cake for doneness by inserting a toothpick into the middle of the cake. If the toothpick comes out clean, the cake is done.
Allow cake to rest for 10-15 minutes. Gently run a knife around the edges of the cake. Put a plate on top of the skillet, and use two hands and invert the cake onto the plate. You may need to tap the bottom of the cake to help release from the pan. Top with fresh cherries.