01 - Preheat oven to 350°F. Grease a 9x13-inch baking dish with cooking spray or butter.
02 - Whisk together pumpkin purée, evaporated milk, eggs, granulated sugar, brown sugar, pumpkin pie spice, salt, and vanilla extract in a large bowl until completely smooth.
03 - Pour the pumpkin mixture into the prepared baking dish and spread into an even layer.
04 - Sprinkle the dry cake mix evenly over the pumpkin mixture, covering the entire surface.
05 - Pour melted butter evenly over the cake mix, ensuring as much coverage as possible.
06 - Sprinkle chopped pecans over the top if desired.
07 - Bake for 45–50 minutes until the top is golden brown and a toothpick inserted into the center comes out mostly clean.
08 - Let cool for at least 20 minutes before serving. Serve warm or at room temperature, optionally topped with whipped cream or vanilla ice cream.