01 - Preheat oven to 350°F (175°C). 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 the mixture is smooth and homogeneous.
03 - Pour the prepared pumpkin mixture evenly into the greased baking pan, smoothing the surface with a spatula.
04 - Sprinkle the dry yellow cake mix in an even layer over the pumpkin mixture. Do not stir or mix.
05 - Slowly drizzle the melted unsalted butter over the entire surface, aiming to cover as much of the cake mix as possible.
06 - Scatter the chopped pecans over the top of the cake, if using.
07 - Bake in the preheated oven for 45 to 55 minutes, or until the surface is golden brown and the center is set. The dessert will continue to firm as it cools.
08 - Allow to cool in the pan for at least 30 minutes before serving. Serve warm or chilled with optional whipped cream or vanilla ice cream.