Make the apple cinnamon topping: Heat a medium saucepan over medium heat and melt the butter. Add the rest of the topping ingredients, and cook until the apples have softened to your liking, stirring occasionally, about 12 to 15 minutes. Let cool slightly.
In a medium bowl, whisk the flour, baking powder, baking soda, Kosher salt, and the 3 tablespoons of sugar. Set aside.
In another large bowl, whisk the eggs, buttermilk, and melted butter until evenly combined.
Add the prepared dry ingredients into the wet ingredients. Mix until just combined and no pockets of flour remain. Do not overmix. The batter should be lumpy and thick.
Heat an electric griddle to about 350 degrees. Add a bit of butter and lightly wipe it so only a thin film of grease remains.
Pour ⅓ cup of batter for each pancake onto the griddle. Then add 2 thin slices of apple on top of each pancake, slightly pushing them down. Cook until the bubbles formed on top begin to pop, and the bottom is golden brown. Then, flip and cook the other side for another minute or so.
Repeat with the remaining batter. Tip: To keep pancakes warm, transfer them to a slightly warm oven.
Serve the pancakes with the warm apple cinnamon topping. If desired, drizzle more maple syrup on top. Enjoy!