01 - Preheat the oven to 350°F. Grease a 9x13-inch baking pan thoroughly.
02 - In a large mixing bowl, whisk together pumpkin puree, sweetened condensed milk, eggs, pumpkin pie spice, granulated sugar, and salt until smooth and fully blended.
03 - Pour the pumpkin mixture into the greased pan and spread it evenly with a spatula.
04 - Evenly distribute the dry yellow cake mix over the pumpkin base. Do not mix or stir.
05 - Drizzle the melted unsalted butter uniformly over the surface, making sure to cover most of the cake mix. Sprinkle chopped pecans on top if using.
06 - Bake in the center of the oven for 45 to 55 minutes, until the top is golden brown and the center is set.
07 - Allow to cool for at least 30 minutes before slicing. Serve warm or chilled, optionally with whipped cream or vanilla ice cream.