In a small saucepan over medium heat, melt 2 tablespoons of butter. Add the finely diced apple, brown sugar, ground cinnamon, and 1/4 cup water. Stir to combine.

Bring to a gentle simmer, then reduce heat to low and cook for 5-7 minutes, or until apples are tender and the sauce has slightly thickened. Set aside and keep warm.

In a large mixing bowl, whisk together the flour, granulated sugar, baking powder, baking soda, salt, and 1 teaspoon ground cinnamon until well combined.

In a separate small bowl, whisk together the buttermilk, milk, egg, and melted butter until smooth.

Pour the wet ingredients into the dry ingredients. Stir gently with a whisk or spatula until just combined. The batter will be slightly lumpy; do not overmix. Fold in the 1/2 medium finely diced apple into the batter.

Heat a large skillet or electric griddle over medium heat. Lightly grease with a little butter or cooking spray. (A good test is to drop a tiny bit of water on the surface; it should sizzle and evaporate quickly).

Pour about 1/4 cup of batter per pancake onto the hot griddle. Cook for 2-3 minutes per side, or until golden brown and bubbles begin to form on the surface, and the edges look set. Flip carefully with a spatula.

Cook for another 1-2 minutes on the second side, until cooked through. Repeat with the remaining batter, greasing the griddle as needed.

Serve the fluffy Apple Cinnamon Pancakes immediately, stacked high, topped with the warm apple cinnamon topping (if using), a pat of butter, and a drizzle of maple syrup.