01 - Preheat oven to 350°F. Grease a 9x13-inch baking pan thoroughly.
02 - Prepare 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 wooden spoon handle, poke holes evenly across cake surface, spacing about 1 inch apart.
04 - Whisk pudding mix and cold milk in medium bowl for 2 minutes until slightly thickened. Stir in peanut butter until smooth and fully incorporated.
05 - Pour peanut butter pudding mixture evenly over warm cake, spreading gently to fill all holes. Cover and refrigerate for 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 completely smooth, heating for additional 10 seconds if needed. Drizzle generously over whipped cream layer.
08 - Sprinkle chopped peanuts and halved peanut butter cups over top if desired. Refrigerate for 30 minutes before serving to allow flavors to meld.