Preheat oven to 350°F. Spray a 13x9 inch baking dish with nonstick spray.
In a large bowl, whisk together the milk and pudding mix until smooth.
Add the cake mix and stir until fully combined. The batter will be very thick.
Fold in the chopped peanut butter cups until evenly distributed.
Spread the batter evenly into the prepared baking dish.
Bake for 25 minutes, or until a toothpick inserted in the center comes out clean.
Allow dump cake to cool before slicing and serving.
Store leftovers covered at room temperature for up to 5 days.
Enjoy this easy and delicious peanut butter cup dump cake!