01 - Preheat oven to 350°F. Grease a 9x13-inch baking dish thoroughly with cooking spray or butter.
02 - In a large bowl, whisk together pumpkin purée, evaporated milk, eggs, granulated sugar, brown sugar, pumpkin pie spice, salt, and vanilla extract until completely smooth and well combined.
03 - Pour the pumpkin mixture into the prepared baking dish and spread evenly across the bottom using a spatula.
04 - Sprinkle the dry cake mix evenly over the pumpkin mixture, ensuring complete coverage without pressing down.
05 - Drizzle the melted butter evenly over the cake mix, covering as much surface area as possible to create the crumb topping.
06 - Sprinkle with chopped pecans evenly across the top if desired.
07 - Bake for 45–50 minutes, or until the top is golden brown and a toothpick inserted into the center comes out mostly clean (some moist crumbs are acceptable).
08 - Allow to cool for at least 20 minutes before serving. Serve warm or at room temperature, optionally topped with whipped cream or vanilla ice cream.