01 - Preheat your oven to 175°C (350°F). Grease a 23×33 cm (9×13-inch) baking dish with butter or non-stick spray.
02 - Spread the creamy peanut butter evenly over the bottom of the prepared baking dish.
03 - Sprinkle half of the chopped peanut butter cups over the peanut butter layer.
04 - Pour the sweetened condensed milk evenly over the candy layer.
05 - Sprinkle the dry chocolate cake mix evenly over the top. Do not mix.
06 - Drizzle the melted butter over the cake mix, covering as much surface as possible.
07 - Sprinkle the milk chocolate chips and the remaining chopped peanut butter cups over the top.
08 - Bake for 35–40 minutes, or until the top is bubbly and slightly crisp.
09 - Allow the cake to cool for 10–15 minutes before serving. Serve warm, topped with whipped cream or vanilla ice cream if desired.