Preheat oven to 350 degrees F.

Lightly grease a 13-by- 9-inch baking pan.

In a large bowl, combine the cake mix, 1 egg, and 8 tablespoons (1 stick) melted butter, and stir until well blended.

Pat mixture into prepared pan and set aside.

In a stand mixer, or with a hand mixer, beat the cream cheese until smooth.

Add the remaining 2 eggs, and the cocoa powder. Lower the speed of the mixer, and add the powdered sugar.

Continue beating until ingredients are well mixed.

Slowly add the remaining 8 tablespoons (1 stick) of melted butter, and the vanilla, continuing to beat the mixture until smooth.

Stir in nuts with a rubber spatula.

Spread filling over cake mixture in pan.

Bake for 40 to 50 minutes. Be careful not to overcook the cake; the center should still be a little gooey when finished baking.

Let cake partially cool on a wire rack before cutting into pieces.