01 - Preheat oven to 350°F. Generously grease a 9x13-inch baking pan 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 toothpick inserted in center comes out clean.
03 - Let cake cool for 10 minutes. Using handle of wooden spoon, poke holes across entire cake surface, spacing approximately 1 inch apart.
04 - Whisk instant vanilla pudding mix with cold milk in medium bowl for 2 minutes until slightly thickened. Stir in peanut butter until completely smooth and incorporated.
05 - Pour peanut butter pudding mixture evenly over warm cake, using spatula to spread filling into all holes. Cover and refrigerate minimum 1 hour to set.
06 - Beat heavy cream, powdered sugar, and vanilla extract in large bowl until stiff peaks form. Spread whipped cream generously over chilled cake.
07 - Microwave chocolate chips, peanut butter, and heavy cream in small microwave-safe bowl for 30 seconds. Stir until smooth; microwave additional 10 seconds if needed. Drizzle over whipped cream.
08 - Sprinkle chopped peanuts and halved peanut butter cups over top if desired. Refrigerate 30 minutes before serving to allow flavors to meld.