01 - Preheat oven to 350°F. Grease a 9x13-inch baking pan thoroughly with cooking spray or butter.
02 - Prepare the 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 all over the cake surface, spacing approximately 1 inch apart.
04 - In a medium bowl, whisk together 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 evenly over the warm cake, spreading to fill all the holes completely. Cover and refrigerate for at least 1 hour.
06 - In a large bowl, beat heavy cream, powdered sugar, and vanilla extract 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. Garnish with chopped peanuts and halved mini peanut butter cups if desired. Chill for 30 minutes before serving for clean slices.