Add the prepared apples, cinnamon, and butter into a 10" cast-iron pan. Place the pan in a cold oven, then preheat it to 425°F.
Next, add the eggs, milk, vanilla, salt, and maple syrup into a blender. Blend and then add the flour. Blend thoroughly but not long.
Once the oven is completely preheated, remove the apples, quickly stir them with the cinnamon, then pour the batter evenly over the hot apples and butter.
Bake the Dutch Baby for 20 minutes or until it's golden brown and puffy.
Finally, carefully remove the skillet, cut into slices, and serve warm with powdered sugar and maple syrup. Enjoy!