Preheat oven to 350 degrees.
Spray 9 x 13 pan with cooking spray. (I like to use a glass pan)
In a large bowl, whisk the pumpkin puree, evaporated milk, eggs, sugar, pumpkin pie spice and salt together until smooth and well combined.
Pour the pumpkin mixture into the prepared pan.
Sprinkle the entire box of dry cake mix evenly over the top of the pumpkin batter.
Sprinkle the pecans evenly over the cake mix.
Drizzle the melted butter evenly over the entire cake.
Bake for 50-60 minutes (check the cake at about 35-40 minutes and if it's becoming too brown place a piece of tinfoil over the top and continue baking for about 10 minutes or until pumpkin mixture is set.)
Let the cake cool on a wire rack. If you aren't going to serve it right away place it in the refrigerator.
Make the whipped cream topping while the cake is cooling. In a large mixing bowl whip the cream cheese until light with a hand mixer. Add in the whipping cream and whip until it is combined and starting to become thick. Add the powdered sugar and vanilla and whip until smooth. Refrigerate until ready to serve.
When ready to serve you can cut into squares of just spoon the cake out of the pan and top with whipped cream topping or ice cream if desired.
Store covered in the refrigerator for up to 4 days. I would not recommend freezing this cake.