01 - Preheat oven to 350°F. Grease a 9x13-inch baking pan thoroughly with cooking spray or butter.
02 - Prepare chocolate cake mix according to package directions. Pour batter into prepared pan and bake for 30-35 minutes until a toothpick inserted in the center comes out clean.
03 - Let cake cool for 10 minutes. Using the handle of a wooden spoon, poke holes all over the cake surface, spacing approximately 1 inch apart.
04 - In a medium bowl, whisk together instant vanilla pudding mix and cold milk for 2 minutes until slightly thickened. Stir in creamy peanut butter until completely smooth and well combined.
05 - Pour peanut butter pudding mixture evenly over the warm cake, using a spatula to spread and ensure the pudding fills all the holes. Cover and refrigerate for at least 1 hour to set.
06 - In a large bowl, beat cold heavy whipping cream, powdered sugar, and vanilla extract with an electric mixer or whisk until stiff peaks form.
07 - Spread whipped cream evenly over the chilled cake, creating a smooth top layer.
08 - Place chocolate chips, peanut butter, and heavy cream in a microwave-safe bowl. Microwave for 30 seconds, then stir until smooth. If needed, microwave for an additional 10 seconds. Drizzle over the whipped cream.
09 - Sprinkle chopped peanuts and halved mini peanut butter cups on top if desired. Refrigerate for 30 minutes before serving to allow flavors to meld.