Preheat the Oven: Preheat your oven to 350°F (175°C). Grease a 9x13-inch baking dish with butter or non-stick spray.
Prepare the Filling: In a large mixing bowl, whisk together the pumpkin puree, evaporated milk, eggs, sugar, pumpkin pie spice, and salt until smooth and well combined.
Layer the Cake: Pour the pumpkin mixture into the prepared baking dish and smooth it out evenly.
Add the Cake Mix: Sprinkle the dry cake mix evenly over the pumpkin filling. Do not mix, just layer it on top like you're covering a casserole.
Add Pecans and Butter: If using, sprinkle chopped pecans over the top. Drizzle the melted butter evenly over everything, making sure to cover the entire surface.
Bake: Bake in the preheated oven for 60-75 minutes, or until the top is golden brown and the edges are bubbly. The center should be soft and custard-like, similar to a pumpkin pie filling.
Cool and Serve: Let the cake cool for 15-20 minutes before serving. It’s perfect served warm with vanilla ice cream, whipped cream, or even enjoyed cold!