01 - Preheat oven to 350°F. Grease a 9x13-inch baking pan thoroughly.
02 - Prepare chocolate cake mix according to package directions. Pour batter into prepared pan and bake for 30–35 minutes, or until a toothpick inserted in the center comes out clean.
03 - Allow cake to cool for 10 minutes. Using the handle of a wooden spoon, poke holes all over the cake, spacing about 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 smooth and well combined.
05 - Pour peanut butter pudding evenly over the cake, spreading to fill all holes. 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 over chilled cake.
07 - Microwave chocolate chips, peanut butter, and heavy cream in a small bowl for 30 seconds. Stir until smooth; microwave for an additional 10 seconds if necessary. Drizzle over whipped cream layer.
08 - Garnish with chopped peanuts and mini peanut butter cups if desired. Chill for 30 minutes before serving for best results.