Step 1: Preheat your oven to 350°F (175°C). Lightly grease a 9x13-inch baking dish with non-stick spray.
Step 2: In a large bowl, whisk together the pumpkin puree, evaporated milk, granulated sugar, pumpkin pie spice, and salt until smooth and well combined.
Step 3: Pour the pumpkin mixture evenly into the prepared baking dish, spreading it to cover the bottom.
Step 4: Evenly sprinkle the dry cake mix over the pumpkin layer. Do not mix it into the pumpkin. Try to create as even a layer as possible.
Step 5: Arrange the thinly sliced cold butter pieces over the dry cake mix, covering as much of the surface as possible. The butter will melt and moisten the cake mix during baking.
Step 6: Bake for 50-60 minutes, or until the topping is golden brown and the pumpkin layer is set (a knife inserted into the center should come out mostly clean).
Step 7: Remove the pumpkin dump cake recipe from the oven and let it cool on a wire rack for at least 15-20 minutes before serving. This allows it to set up for easier scooping.