Spray a 9x13 baking pan with nonstick cooking spray and line the bottom with parchment paper This step is necessary in order for the cake to come out of the pan. Set aside.
Beat pumpkin, evaporated milk, white sugar, eggs and vanilla in a mixer until well combined. Pour into prepared pan. Sprinkle with cake mix and drizzle with butter. Top with chopped pecans.
Bake for 60 minutes or until edges are bubbling and center is set. Cool completely in the pan. Invert the cake onto a large serving platter and remove the parchment.
Beat cream cheese, powdered sugar and vanilla in a mixing bowl until smooth. Fold in whipped topping. Frost cake. Cut into 24 slices and serve.