Prepare the Cake Layer: Preheat your oven to 350°F (175°C). Prepare the chocolate cake mix according to the package instructions. Pour the batter into a greased 9×13-inch baking dish.

Peanut Butter Cream Cheese Layer: In a medium-sized mixing bowl, beat together the melted butter, peanut butter, and cream cheese until smooth. Gradually add in the powdered sugar and vanilla extract, and continue beating until fully combined.

Assemble the Cake: Drop spoonfuls of the peanut butter cream cheese mixture over the chocolate cake batter. Use a knife to swirl the two mixtures together, creating a marbled effect.

Add the Chips: Sprinkle the chocolate chips, peanut butter chips, and chopped peanuts (if using) evenly over the top of the cake.

Bake: Place the baking dish in the preheated oven and bake for 35-40 minutes, or until a toothpick inserted into the center comes out mostly clean with a few moist crumbs.

Cool and Serve: Allow the cake to cool completely in the baking dish on a wire rack. Once cooled, slice into squares and serve.