Heat the oven to 350°F and grease a 9 x 13-inch baking pan. Prepare the chocolate cake mix with the eggs, water, and vegetable oil listed on the package, then spread the batter evenly in the pan.

Bake the cake for approximately 30–35 minutes, or follow the timing on the cake-mix package. Test the center with a toothpick; it is ready when the toothpick comes out clean.

Let the cake cool for about 10–15 minutes. Using the handle of a wooden spoon or a large straw, make holes throughout the cake about 1 inch apart.

Slowly pour the sweetened condensed milk over the cake, aiming for the holes so the filling can sink below the surface. Pour the caramel topping over the cake and spread it evenly; warm thick caramel briefly if needed so it pours more easily.

Allow the cake to cool completely before adding the topping. This prevents the whipped topping from melting and keeps the finished dessert light rather than runny.

Spread the thawed whipped topping over the cooled cake in an even layer. Scatter the chopped candy bars across the top, pressing a few pieces lightly into the topping if desired.

Refrigerate the cake for at least 1 hour before serving, or chill it overnight for an even firmer texture. Keep the cake covered and refrigerated after serving.