Heat the oven to 350°F (175°C) and grease a 9 x 13-inch baking pan. Prepare the chocolate cake mix with the eggs, water, and vegetable oil according to the package directions, then spread the batter evenly in the pan.

Bake for 28–33 minutes, or until the center springs back lightly and a toothpick comes out with only a few moist crumbs. Let the cake cool in the pan for approximately 10–15 minutes.

Use the handle of a wooden spoon or a large straw to poke holes across the cake. Pour the caramel topping over the surface, spreading it gently so it flows into the holes without pooling heavily in one area.

Allow the cake to cool completely before adding the topping. Whisk the instant chocolate pudding mix with the cold whole milk for about 2 minutes, then fold in the thawed whipped topping.

Spread the chocolate pudding mixture over the cooled cake in an even layer. Scatter the chopped Twix bars over the top, then add extra caramel sauce or mini chocolate chips if desired.

Refrigerate the finished cake for at least 1 hour before slicing. For the cleanest pieces, chill it for several hours or overnight and use a sharp knife warmed under hot water and dried before each cut.