Preheat the oven to 350°F. If using a glass baking pan, preheat the oven to 325°F.
Grease a 9x12-inch baking pan with cooking spray.
In a mixing bowl, combine the German chocolate cake mix, melted butter, and egg.
Beat until the ingredients are fully combined and a thick dough forms.
Transfer the cake mixture to the prepared baking pan.
Press the mixture evenly across the bottom of the pan to form the base layer.
Cut each large peanut butter cup into 4 pieces.
Roughly chop the Butterfinger candy bars.
Scatter the peanut butter cup pieces and chopped Butterfinger bars evenly over the cake layer.
In a separate large mixing bowl, combine the softened cream cheese, peanut butter, and vanilla extract.
Beat until the mixture is smooth and evenly blended.
Add the eggs one at a time, mixing well after each addition.
Pour in the melted butter and continue mixing until fully incorporated.
Add the confectioners’ sugar gradually.
Mix until the cream cheese layer is smooth, thick, and fully combined.
Spread the cream cheese mixture evenly over the candy layer.
Bake for approximately 50 minutes, or until the center is puffed and only slightly jiggly.
If using a glass pan, the cake may require slightly more than 1 hour of baking time.
Remove the cake from the oven and allow it to cool completely.
Place the chocolate chips in a microwave-safe bowl.
Microwave for 1 minute, then stir.
Add the vegetable oil or canola oil to the melted chocolate.
Stir until the chocolate is smooth and fully combined.
Spread the chocolate topping evenly over the cooled cream cheese layer.
Allow the chocolate topping to set slightly before slicing.
Cut into squares and serve.