Preheat oven to 425 degrees. Put butter in a 12 inch cast iron pan and place in the oven to melt. The pan needs to be screaming hot, so this is an important step. Don’t skip it! While the butter melts mix everything else together. When the butter is melted in the pan, take it out and pour the batter in. Place it back into the oven and let it bake 18-20 minutes. While the pancake is baking, warm your pie filling in a small saucepan. Spread over the pancake as soon as it comes out of the oven.