Preheat oven to 350. Prepare a 13x9in baking pan by greasing bottom and sides.
Mix together, in a medium-sized bowl, Peanut Butter Chocolate Chip Dip Mix, 1 large egg beaten, and 16 oz of softened cream cheese. Mix well, set aside
Mix together in a large, mixing bowl Dark Chocolate Cake Mix, water, 3 large eggs (beaten), vegetable oil, and peanut butter. Mix with an electric mixer for 2 minutes on medium speed. Pour cake batter into 13x9in, greased pan. Spread batter evenly in pan.
Place spoonfuls of prepared Peanut Butter Chocolate Chip Dip mixture evenly on top of cake batter. Using a butter knife, cut through the filling into the cake batter marbling the two together. Work lengthwise and then side to side. Bake for approx 50 minutes or until cake springs back and peanut butter chocolate chip filling appears dry on top. Allow cake to cool for 15 minutes.
Remove foil liner completely from tub of frosting. Microwave for 50 seconds. Stir melted frosting in tub and pour over baked cake. Allow to cool for 1 hour. Cover and refrigerate. This cake is best when allowed to sit 8 hours/ overnight before serving. Store cake in refrigerator. This cake requires refrigeration because of filling.