Creating the Easy Skillet Upside Down Apple Pancake is straightforward. Just follow these simple steps:

1. Preheat Oven: Begin by preheating your oven to 400°F (200°C).
2. Prepare the Skillet: In a 10-inch cast-iron skillet, melt the butter over medium heat, swirling to coat the bottom and sides evenly.
3. Caramelize Apples: Add the sliced apples to the skillet, then sprinkle brown sugar and cinnamon over them. Cook for about 5 minutes until the apples soften slightly.
4. Mix Dry Ingredients: In a separate bowl, whisk together the flour, granulated sugar, baking powder, and salt until well combined.
5. Combine Wet Ingredients: In another bowl, mix the milk, egg, and vanilla extract until combined.
6. Combine Mixtures: Gradually add the wet ingredients to the dry ingredients, stirring until just combined. Be careful not to overmix; a few lumps are fine.
7. Pour Batter: Carefully pour the batter over the caramelized apples in the skillet, spreading it evenly.
8. Bake: Place the skillet in the preheated oven and bake for 15-20 minutes, or until the pancake is puffed and golden brown.
9. Cool Slightly: Once baked, remove the skillet from the oven and let it cool for about 5 minutes.
10. Flip the Pancake: Carefully invert the skillet onto a large plate to flip the pancake so the apples are on top.

Following these steps should lead to a beautifully cooked pancake that impresses everyone at the table.