1. Preheat your oven to 350°F (175°C). Grease a 9×13-inch baking dish with butter or non-stick spray.
2. In a large mixing bowl, combine the pumpkin puree, granulated sugar, brown sugar, eggs, vanilla extract, cinnamon, and salt. Stir until the mixture is smooth and well combined.
3. Pour the pumpkin mixture into the prepared baking dish, spreading it evenly across the bottom.
4. Sprinkle the yellow cake mix evenly over the pumpkin mixture. Do not stir. The cake mix should sit on top as a separate layer.
5. Drizzle the melted butter evenly over the top of the cake mix, ensuring that most of the dry areas are covered to help create a crispy, buttery topping.
6. Sprinkle the chopped pecans evenly over the top of the buttered cake mix.
7. Bake in the preheated oven for 50 to 60 minutes or until the top is golden brown and the pecans are toasted. The edges should start to pull away from the sides of the dish.
8. Allow the cake to cool slightly before serving, letting the flavors meld together.

From my experience, the key to this cake is patience. Allowing it to cool just a bit will make serving easier and enhance the overall flavor profile.