01 - Preheat oven to 350°F. Lightly grease a 9x13-inch baking pan to prevent sticking.
02 - In a large mixing bowl, whisk together pumpkin puree, sweetened condensed milk, eggs, pumpkin pie spice, granulated sugar, and salt until the mixture is completely smooth.
03 - Pour the pumpkin mixture into the prepared baking pan, spreading evenly with a spatula.
04 - Evenly distribute the dry yellow cake mix over the pumpkin layer without stirring.
05 - Drizzle melted unsalted butter across the entire surface to moisten the cake mix thoroughly.
06 - Sprinkle chopped pecans evenly over the top if using.
07 - Bake for 45 to 55 minutes, or until the top becomes golden brown and the center is set. The dessert will firm up as it cools.
08 - Allow to cool for at least 30 minutes. Serve warm or chilled. Garnish with whipped cream or vanilla ice cream if desired.