Preheat oven to 350°F.
Spray a 9x13 pan with nonstick spray.
In a large bowl place the cake mix ingredients(substituting milk for water). My cake mix called for ½ cup vegetable oil, 1 cup water, and 3 eggs. I substituted one cup of milk in place of the water.)
Mix per the package instructions. For my cake mix, it was on medium for two minutes.
Pour the cake batter into the prepared 9x13 pan. Set aside.
In a medium-sized bowl place the pumpkin puree, evaporated milk, 1 teaspoon of pumpkin pie spice, eggs, and brown sugar. Whisk together until smooth.
SLOWLY pour the pumpkin mixture right on top of the cake mix, over the whole cake. The key is to pour this slowly and drizzle it all over the top of the cake, along the edges so it covers the top. It will already begin to sink.
Bake for 50 minutes to one hour or until no longer loose in the middle.
While the cake is cooling in a large bowl whisk together the pudding mix, milk, and remaining 1 teaspoon of pumpkin pie spice until smooth.
Fold in the Cool Whip until combined.
Spread over the cooled cake.
Refrigerate until ready to serve.