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 evenly across the entire cake surface, spacing approximately 1 inch apart.
04 - Whisk together 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 and well combined.
05 - Pour peanut butter pudding mixture evenly over the warm cake, spreading gently to ensure all holes are filled. Cover and refrigerate for at least 1 hour until set.
06 - Beat heavy cream, powdered sugar, and vanilla extract in a large bowl until stiff peaks form. Spread whipped cream evenly over the chilled cake.
07 - Microwave chocolate chips, peanut butter, and heavy cream in a small microwave-safe bowl 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 layers to set before slicing and serving.