1. Preheat oven to 350º. Butter 9x13 inch baking pan.
2. In a large bowl, whisk together the pumpkin puree, evaporated milk, eggs, sugars, vanilla, pumpkin pie spice and salt. Mix well combined until smooth.
3. Pour mixture into prepared pan and spread into an even layer.
4. Sprinkle dry cake mix evenly over the pumpkin mixture and use your hands to gently press it into the batter.
5. Sprinkle the top of the cake with chopped pecans and evenly drizzle the melted butter over the entire cake.
6. Bake in preheated oven for 40 minutes. At this point, check your cake. If the top is becoming brown, cover the cake with a piece of foil for the remaining baking time. Continue baking an additional 10-20 minutes or until set.
7. Remove pan to a wire rack to cool completely. Chill for a few hours before serving.
8. If desired, top with whipped cream and chopped pecans before serving.