1. Preheat oven to 350 degrees Fahrenheit. 2. To make the cake, combine the yellow cake mix, the melted butter, and the egg with an electric mixer. 3. Pat the mixture into the bottom of a lightly greased 13 by 9 inch pan. 4. For the filling: Beat the cream cheese and the sweet potato puree with a mixer until smooth. Mix in the eggs, vanilla, butter, cinnamon, and nutmeg until well combined. 5. Add the powder sugar and mix slowly until it is well incorporated. 6. Pour the filling over the cake batter and bake for 50 - 55 minutes.