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 evenly across cake surface, spacing approximately 1 inch apart.
04 - Whisk pudding mix and cold milk in medium bowl for 2 minutes until slightly thickened. Stir in peanut butter until completely smooth and combined.
05 - Pour peanut butter pudding mixture evenly over cake, using spatula to spread filling into all holes. Cover and refrigerate for at least 1 hour.
06 - Beat heavy cream, powdered sugar, and vanilla extract in large bowl until stiff peaks form. Spread whipped cream evenly over chilled cake surface.
07 - Microwave chocolate chips, peanut butter, and heavy cream in small bowl for 30 seconds. Stir until smooth, microwaving additional 10 seconds if needed. Drizzle over whipped cream layer.
08 - Sprinkle chopped peanuts and arrange halved peanut butter cups on top if desired. Refrigerate 30 minutes before serving.