Preheat oven to 350 degrees F (175 degrees C). Place butter in a large iron skillet and place in preheating oven until melted, about 5 minutes.
Stir brown sugar into melted butter and place back in oven until bubbling, about 5 minutes.
Gently lay 1 pie crust on top of butter-brown sugar mixture, without pressing crust down. Arrange apple slices on top of pie crust.
Mix white sugar, cinnamon, and flour together in a bowl; sprinkle over apple slices. Place the remaining pie crust over apple slices, making slits in the top crust for ventilation. Seal the 2 crusts together.
Bake in the preheated oven until top crust is lightly browned, about 45 minutes.