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 all over cake at 1-inch intervals.
04 - Whisk pudding mix and cold milk in medium bowl for 2 minutes until slightly thickened. Stir in peanut butter until completely smooth.
05 - Pour peanut butter pudding evenly over cake, spreading to fill all holes. Cover and refrigerate at least 1 hour.
06 - Beat heavy cream, powdered sugar, and vanilla extract in large bowl until stiff peaks form. Spread whipped cream over chilled cake.
07 - Microwave chocolate chips, peanut butter, and heavy cream in small bowl for 30 seconds. Stir until smooth, adding 10 more seconds if needed.
08 - Drizzle chocolate mixture over whipped cream. Garnish with chopped peanuts and halved peanut butter cups if desired.
09 - Refrigerate for 30 minutes before serving to allow flavors to meld.