01 - Preheat the oven to 350°F. Grease a 9x13-inch baking pan thoroughly.
02 - Whisk together pumpkin puree, sweetened condensed milk, eggs, pumpkin pie spice, granulated sugar, and salt in a large mixing bowl until completely smooth and combined.
03 - Pour the pumpkin mixture into the prepared baking pan, spreading it into an even layer.
04 - Sprinkle the dry yellow cake mix evenly over the entire pumpkin layer. Do not stir.
05 - Slowly drizzle the melted butter evenly over the cake mix, covering as much of the surface as possible.
06 - Scatter the chopped pecans evenly over the top, if using.
07 - Transfer to the oven and bake for 45 to 55 minutes, until the surface is golden brown and the center is set.
08 - Let cool at least 30 minutes before serving. Serve warm or chilled, optionally garnished with whipped cream or vanilla ice cream.