For the skillet apple pie: Preheat the oven to 400 degrees F.
Melt the butter in a 9-inch cast-iron skillet; set aside 1 tablespoon of the melted butter for the top crust. To the melted butter, add the brown sugar and melt them together on medium heat, about 2 minutes. Remove from the heat and line the skillet with one of the pie crusts. Pour the apple pie filling over the crust and sprinkle with 1 tablespoon of the cinnamon sugar. Use the second pie crust to cover the filling. Brush the top with the reserved melted butter, then evenly sprinkle the remaining 1 tablespoon cinnamon sugar on top. Cut vents in the middle of the pie. Bake for 30 minutes. Serve hot, topped with a generous dollop of cinnamon whipped cream.
For the cinnamon whipped cream: Chill a large metal mixing bowl and a wire beater attachment in the freezer for about 20 minutes. Pour the cream, cinnamon and sugar into the cold mixing bowl and beat until soft peaks form, 2 to 3 minutes; the mixture should hold its shape when dropped from a spoon. Don't overbeat or you'll have sweetened butter!