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 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 evenly across the entire cake surface, spacing about 1 inch apart.
04 - In a medium bowl, whisk together instant vanilla pudding mix and cold milk for 2 minutes until slightly thickened. Stir in creamy peanut butter until completely smooth and combined.
05 - Pour peanut butter pudding mixture evenly over the warm cake, using a spatula to spread pudding into all the holes. Cover and refrigerate for at least 1 hour to set.
06 - In a large bowl, beat heavy cream, powdered sugar, and vanilla extract with an electric mixer until stiff peaks form. Spread whipped cream evenly over the chilled cake.
07 - Place chocolate chips, peanut butter, and heavy cream in a microwave-safe bowl. Microwave for 30 seconds, stir until smooth. Microwave for an additional 10 seconds if needed to achieve pourable consistency.
08 - Drizzle chocolate mixture over the whipped cream layer. Sprinkle with chopped roasted peanuts and halved mini peanut butter cups if desired.
09 - Refrigerate completed cake for 30 minutes to allow flavors to meld and drizzle to set before serving.