Preheat oven to 350°F (175°C). Grease and flour a 9x13 inch baking pan. Prepare the chocolate cake mix according to package directions. Pour batter into the prepared pan and bake as directed, or until a toothpick inserted into the center comes out clean.

Let the cake cool on a wire rack for 15 minutes. The cake should still be warm. Use the handle of a wooden spoon to poke holes all over the top of the cake, about 1-2 inches apart.

In a small saucepan over low heat, combine the sweetened condensed milk and 1 cup of creamy peanut butter. Stir until smooth and pourable. Do not boil.

Immediately and carefully pour the warm peanut butter filling over the warm cake, spreading it evenly so it soaks into the holes.

Allow the cake to cool to room temperature. Then, cover and refrigerate for at least 4 hours or overnight to allow the filling to set.

Once chilled, spread the thawed whipped topping over the cake. Drizzle with chocolate syrup and melted peanut butter, then sprinkle with chopped peanut butter cups. Slice and serve cold.