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 surface at 1-inch intervals.
04 - Whisk instant vanilla pudding mix and cold milk in a medium bowl for 2 minutes until slightly thickened. Stir in creamy peanut butter until completely smooth.
05 - Pour peanut butter pudding mixture evenly over the warm cake, using a spatula to spread filling into all the holes. Cover and refrigerate for at least 1 hour.
06 - Beat cold heavy cream, powdered sugar, and vanilla extract in a large bowl until stiff peaks form. Spread whipped cream evenly over the chilled cake.
07 - Combine chocolate chips, peanut butter, and heavy cream in a microwave-safe bowl. Microwave for 30 seconds, stir until smooth. Microwave for additional 10 seconds if needed.
08 - Drizzle chocolate mixture over the whipped cream layer. Garnish with chopped peanuts and halved peanut butter cups if desired. Refrigerate for 30 minutes before serving.