Preheat the oven to 350°F (175°C) and grease a 9x13-inch baking dish. Whisk the pumpkin purée, evaporated milk, eggs, sugar, and pumpkin pie spice until smooth, then pour into the prepared dish.

Sprinkle the dry cake mix evenly over the pumpkin layer. Drizzle melted butter over the top, covering as much of the surface as possible. Do not stir.

Scatter pecans over the top. Bake for 50 to 55 minutes, until deep golden brown and the edges bubble, with a slight wobble in the center.

Cool on a wire rack for at least 20 minutes before scooping. Serve warm with vanilla ice cream or whipped cream.