01 - Preheat oven to 350°F and lightly grease a 9x13-inch baking pan.
02 - In a large mixing bowl, thoroughly whisk together pumpkin puree, sweetened condensed milk, eggs, pumpkin pie spice, granulated sugar, and salt until fully blended.
03 - Pour the pumpkin batter into the prepared pan, spreading it evenly with a spatula.
04 - Sprinkle the dry yellow cake mix evenly over the pumpkin layer, ensuring an even distribution; do not mix.
05 - Drizzle melted unsalted butter evenly over the cake mix layer, covering as much of the surface as possible.
06 - Scatter chopped pecans evenly over the top of the cake (optional).
07 - Transfer to the oven and bake for 45 to 55 minutes, or until the topping is golden brown and the center feels set.
08 - Remove from oven and cool in the pan for at least 30 minutes before serving. Serve warm or chilled, with whipped cream or vanilla ice cream if desired.