Step 1: Preheat your oven to 350°F (175°C) and grease a 9x13 inch baking dish with non-stick spray.
Step 2: In a large mixing bowl, whisk together the pumpkin puree, evaporated milk, eggs, sugar, pumpkin pie spice, and salt until smooth and well combined.
Step 3: Pour the pumpkin mixture into the prepared baking dish and spread it out evenly.
Step 4: Sprinkle the dry yellow cake mix evenly over the top of the pumpkin mixture. Do not stir it in.
Step 5: If using pecans, sprinkle them evenly over the cake mix layer.
Step 6: Drizzle the melted butter (or place the butter slices) evenly over the entire surface of the cake mix, ensuring as much coverage as possible.
Step 7: Bake for 50-60 minutes, or until the edges are bubbling and the top is a deep golden brown.
Step 8: Allow the Pumpkin Pie Dump Cake to cool for at least 15-20 minutes before serving to let the custard set.