Preheat the oven to 350°F. Lightly grease a 9x13-inch baking dish.
Arrange the Walker's Shortbread cookies in a single layer across the bottom of the dish. Break a few cookies as needed to fill in any gaps.
Spoon the apple pie filling evenly over the cookie layer.
In a small bowl stir together the dry spice cake mix and pumpkin pie spice. Sprinkle the mixture evenly over the apple filling. Do not mix.
Arrange the thin cold butter slices all over the top covering as much of the cake mix surface as possible.
Bake uncovered for 45 to 50 minutes until the top is golden brown and the filling is hot and bubbly around the edges.
Let cool for 10 to 15 minutes before serving.
Finish with a generous drizzle of caramel sauce and a sprinkle of flaky sea salt if desired.