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 smooth and fully combined.
03 - Pour the pumpkin mixture into the prepared baking pan and spread it evenly with a spatula.
04 - Evenly sprinkle the dry yellow cake mix over the pumpkin layer without stirring.
05 - Drizzle the melted butter evenly across the entire surface of the cake mix, making sure as much of the cake mix is covered as possible.
06 - Scatter the chopped pecans evenly over the top, if using.
07 - Bake in the center of the oven for 45 to 55 minutes until the top is golden brown and the center is set. The cake will firm up as it cools.
08 - Cool for at least 30 minutes before serving. Serve warm or chilled, optionally with whipped cream or vanilla ice cream.