Prepare the Baking Dish: Preheat the oven to 350°F and lightly coat a 9x13-inch baking dish with nonstick spray. This ensures your dump cake won't stick to the pan and will be easy to serve once baked.

Make the Pudding Base: In a large mixing bowl, whisk together the chocolate pudding mix and milk until smooth and slightly thickened. This creates a rich, creamy foundation for your dump cake that will become even more decadent as it bakes.

Layer the Pudding: Spread the pudding mixture evenly into the bottom of the prepared baking dish, making sure it reaches all corners for an even base layer.

Add Cake Mix Layer: Sprinkle the dry chocolate cake mix evenly over the pudding layer, making sure to cover the entire surface. This dry mix will absorb moisture from the pudding and butter as it bakes, creating a cake-like texture.

Add Butter and Toppings: Drizzle the melted butter evenly across the cake mix, letting it soak into the dry spots. Then drop spoonfuls of creamy peanut butter over the top, followed by scattering the chopped peanut butter cups and mini chocolate chips evenly across the surface.

Bake to Perfection: Bake for 40–45 minutes, until the edges are set and the center is gooey and bubbling. The cake will develop a slightly crisp top while maintaining a fudgy interior.

Cool and Serve: Allow the cake to cool for about 15 minutes before serving warm. This brief cooling period helps the layers set slightly while still maintaining that delicious warm, gooey texture. Add whipped cream or a scoop of vanilla ice cream if desired.