Preheat oven to 350 degrees. Lightly grease a large jelly roll pan.
In a medium bowl mix together cake mix, butter, and egg. Press mixture into prepared pan. (tip: use a rolling pin!)
In a large bowl mix pumpkin puree, eggs, evaporated milk, sugar, cinnamon, salt, and pumpkin pie spice until smooth. Spread mixture over cake base layer. Bake for 60 minutes until an inserted toothpick comes out clean.
Allow to cool completely, serve with whipping cream and caramel sauce if desired.