Preheat and Prepare Pan
Preheat your oven to 350°F (175°C). Lightly grease a 9×13-inch baking dish.

Make Pudding Layer
In a medium bowl, whisk together the instant chocolate pudding mix and cold milk until smooth and slightly thickened (about 2 minutes). Pour the pudding into the bottom of the prepared baking dish and spread evenly.

Add Peanut Butter and Candy
Drop dollops of peanut butter over the pudding layer. Use a knife or spatula to lightly swirl it into the pudding. Sprinkle chopped peanut butter cups and mini chocolate chips evenly over the top.

Add Cake Mix Layer
Sprinkle the dry chocolate cake mix evenly over the entire surface—do not stir.

Top with Butter
Arrange thin slices of butter over the dry cake mix to help it bake evenly and create a buttery crust.

Bake the Cake
Bake for 40–45 minutes, or until the top is set and the edges are bubbly. Some gooey spots in the center are okay!

Cool and Serve
Let the cake cool for 10–15 minutes before serving. Top with extra chopped peanut butter cups if desired. Best served warm with a scoop of vanilla ice cream!