Preheat the oven to 350 degrees F (175 degrees C). Spray a 9x13-inch square pan with nonstick spray.
Spread apple pie filling in the prepared pan. Top with cranberry sauce. Sprinkle cake mix evenly over top, then cover cake mix as much as possible with butter slices. Sprinkle with walnuts.
Bake in the preheated oven until a toothpick inserted in the center comes out clean, 50 to 55 minutes. Cool for a least 15 minutes before serving.