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 center comes out clean.
03 - Let cake cool for 10 minutes. Using handle of wooden spoon, poke holes all over cake surface, spacing approximately 1 inch apart.
04 - In medium bowl, whisk together instant vanilla pudding mix and cold milk for 2 minutes until slightly thickened. Stir in peanut butter until completely smooth and combined.
05 - Pour peanut butter pudding mixture evenly over warm cake, using spatula to spread and ensure filling penetrates all holes. Cover and refrigerate for at least 1 hour.
06 - In large bowl, beat heavy cream, powdered sugar, and vanilla extract with electric mixer until stiff peaks form. Spread whipped cream evenly over chilled cake surface.
07 - Place chocolate chips, peanut butter, and heavy cream in microwave-safe bowl. Microwave for 30 seconds, stir until smooth. If needed, microwave additional 10 seconds. Drizzle over whipped cream layer.
08 - Sprinkle chopped peanuts and arrange halved peanut butter cups on top if desired. Refrigerate for 30 minutes before serving to allow flavors to meld.