Make the apple cinnamon topping: heat a medium saucepan to medium heat and cook all the topping ingredients until apples have softened to your liking, about 5-10 minutes. Let cool slightly.
In a medium bowl, mix together the flour, baking powder, baking soda, Kosher salt, and sugar.
In separate bowl, whisk egg whites with an electric mixer at medium high speed, until you get stiff peaks.
In a large large bowl, whisk egg yolks and buttermilk. Mix in the melted butter. With a rubber spatula, fold in the egg whites until just combined.
Add the dry ingredients to the wet mixture and mix the batter, but do not overmix. It should be very lumpy and thick.
Heat an electric griddle to about 350 degrees F for 3 minutes. Coat with butter or oil spray. Using paper towels, gently wipe any excess butter until only a thin film remains.
Pour 1/3 cup of batter for each pancake onto the griddle. Then add 3 slices of apple on top of each pancake, slightly pushing them down. Cook for about 2-3 minutes, until you see bubbles forming on top and sides turn golden brown. Flip and cook for another 2 minutes. Repeat with the remaining batter.
To serve, stack a few pancakes and add your apple cinnamon topping and more maple syrup, if you want. Enjoy!