01 - Preheat oven to 350°F. 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 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 about 1 inch apart.
04 - Whisk together instant vanilla 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 mixture evenly over warm cake, spreading to fill all holes. Cover and refrigerate at least 1 hour until set.
06 - Beat heavy cream, powdered sugar, and vanilla extract in large bowl until stiff peaks form. Spread whipped cream evenly over chilled cake.
07 - Microwave chocolate chips, peanut butter, and heavy cream in small bowl for 30 seconds. Stir until smooth, microwaving additional 10 seconds if needed.
08 - Drizzle chocolate mixture over whipped cream layer. Sprinkle chopped peanuts and arrange peanut butter cups on top if desired.
09 - Refrigerate assembled cake for 30 minutes before serving to allow flavors to meld and layers to set.