Step 1: Preheat your oven according to the directions on the chocolate cake mix box. Grease a 9x13-inch baking dish.
Step 2: Combine the cake mix with the required ingredients (typically eggs, oil, and water) in a large bowl. Mix until smooth.
Step 3: Pour the batter evenly into the prepared baking dish and bake according to the box instructions, usually around 30-35 minutes, or until a wooden skewer comes out clean.
Step 4: Let the cake cool for about 10-15 minutes on a wire rack. While still warm, use the handle of a wooden spoon to poke holes all over the cake, spaced evenly. These holes should reach most of the way through the cake, but not to the bottom.
Step 5: In a separate bowl, combine the sweetened condensed milk and 1/2 cup creamy peanut butter. Mix until smooth and fully blended.
Step 6: Pour the filling evenly over the warm cake, making sure it flows into all the holes. Let the cake cool completely at room temperature.
Step 7: Once the cake has fully cooled, spread the thawed whipped topping evenly over the entire surface.
Step 8: Drizzle the melted 1/2 cup peanut butter and chocolate syrup over the whipped topping.
Step 9: Finish by sprinkling the chopped Reese’s peanut butter cups generously on top.
Step 10: Refrigerate the cake for at least 2 hours to set (preferably overnight for best results).
Step 11: Slice and serve chilled.