Preheat your oven to 350°F (175°C). Grease and flour a 9x13 inch baking pan. Prepare the chocolate cake mix according to the 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 for 15 minutes.

While the cake is still warm, use the rounded handle of a wooden spoon to poke holes all over the top, about an inch apart. In a small saucepan over low heat, combine the sweetened condensed milk and 1/2 cup of creamy peanut butter. Stir until melted and smooth. Pour the warm filling evenly over the cake.

Allow the cake to cool completely, then transfer to the refrigerator to chill for at least 2 hours.

In a large bowl, beat the softened cream cheese and 1 cup of peanut butter with an electric mixer until smooth. Gradually beat in the powdered sugar. Gently fold in the thawed whipped topping until light and fluffy.

Spread the peanut butter frosting evenly over the chilled cake. Sprinkle with chopped peanut butter cups. Refrigerate for at least another hour before serving for best results.