Preheat the oven to 350ºF (180ºC). Lightly grease a 9-x-13-inch (35-x-24-cm) baking pan with baking spray.
In a large bowl, combine canned pumpkin, evaporated milk, sugar, pumpkin spice, sugar; Mix until well blended. Sprinkle the cornstarch on top and mix until well incorporated and no lumps.
Pour the pumpkin mixture into your prepared baking dish.
Sprinkle a package of dry yellow cake mix over the top, spreading evenly.
Top with chopped pecans and evenly drizzle the melted butter over the entire cake.
Bake for about 45-50 minutes, or until the top is set and golden brown and the edges are set. The center will be wobbly. Note: when you nudge your cake, the filling should be firmer around the edges but still jiggle in the center. If in doubt, insert a knife into the edge of the filling comes out moist but clean. It doesn’t have to be bone dry right out of the oven—remember, the filling continues to set as it cools.
Remove pan from the oven to a wire rack to cool completely. Allow cooling before serving.
You can serve this cake topped with whipped cream or vanilla ice cream.