01 - Preheat oven to 350°F. Grease a 9x13-inch baking pan with butter or nonstick spray.
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 homogenous.
03 - Pour the pumpkin filling evenly into the prepared baking pan, smoothing the surface with a spatula.
04 - Sprinkle the dry yellow cake mix evenly over the pumpkin layer, ensuring full coverage without mixing into the pumpkin layer.
05 - Drizzle melted butter uniformly over the cake mix to moisten the surface as thoroughly as possible.
06 - Distribute chopped pecans over the top if desired for added texture.
07 - Bake for 45 to 55 minutes, or until the top is golden and the center has set. The dessert will firm further as it cools.
08 - Cool for at least 30 minutes before cutting. Serve warm or chilled, optionally with whipped cream or vanilla ice cream.