Preheat oven to 400 degrees F. At the same time, place a 10-inch cast iron skillet in the oven to get it really hot.
Make the caramelized apples: In a skillet, combine the sliced apples with butter, brown sugar, maple syrup, and ground cinnamon. Cook over medium heat, stirring, for about 15 minutes, or until softened and caramelized. Set aside.
Make the batter: In a blender, combine the eggs, flour, milk, and granulated sugar. Blend until well combined and smooth. The batter should be thin and free of lumps.
Carefully, remove hot cast iron skillet from oven. Melt the 2 tablespoons of butter in the hot skillet, swirling it around to coat and cover the pan. It should sizzle.
Then, immediately add the pancake batter and return to the oven. Bake for about 18 to 20 minutes, or until puffed up and golden brown. The edges should be crispy. Note: Do not open the oven before time is up, it will deflate the pancake. Instead, use the oven light and peek through the window.
To serve, top with the caramelized apples and more maple syrup, if needed. Dust with confectioners sugar. Enjoy!