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 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 creamy peanut butter until completely smooth and combined.
05 - Pour peanut butter pudding mixture evenly over warm cake, using spatula to spread pudding into all holes. Cover and refrigerate for minimum 1 hour until set.
06 - Beat cold heavy whipping cream with 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 microwave-safe bowl for 30 seconds. Stir vigorously until smooth. Microwave additional 10 seconds if needed for consistency.
08 - Drizzle warm chocolate mixture over whipped cream layer. Sprinkle with chopped roasted peanuts and halved mini peanut butter cups if desired.
09 - Refrigerate completed cake for 30 minutes before serving to allow flavors to meld and layers to set properly.