01 - Set oven to 350°F and grease a 9x13-inch baking pan to prevent sticking.
02 - In a large mixing bowl, vigorously whisk together pumpkin puree, sweetened condensed milk, eggs, pumpkin pie spice, sugar, and salt until smooth and homogeneous.
03 - Transfer the pumpkin mixture into the greased baking pan, spreading it evenly across the bottom.
04 - Evenly sprinkle the dry yellow cake mix over the pumpkin base, ensuring full coverage without mixing layers.
05 - Drizzle melted unsalted butter evenly over the cake mix layer, covering as much surface as possible for even browning.
06 - Distribute chopped pecans evenly over the top if using.
07 - Bake in the center rack for 45 to 55 minutes until the top is golden brown and the center feels set when lightly pressed.
08 - Allow to cool for at least 30 minutes before slicing. Serve warm or chilled, optionally topped with whipped cream or vanilla ice cream.