Follow the instructions on the cake mix packaging to prepare the batter, incorporating the required eggs, oil, and water. Pour the mixture into a 9x13-inch (23x33 cm) baking pan and bake as directed. Once fully baked, allow the cake to cool entirely, then slice into 1-inch cubes.

In a medium mixing bowl, vigorously whisk together the instant chocolate pudding mix and cold milk for about 2 minutes, or until it reaches a thick, smooth consistency. Allow it to rest briefly to continue setting.

Using a large trifle bowl or a deep glass serving dish, begin by placing half of the chocolate cake cubes at the bottom. Spoon half of the prepared pudding over the cake, spreading it evenly. Follow with a layer of half the whipped topping, smoothing it out gently. Scatter half of the crushed toffee pieces across the top.

Repeat the process with the remaining cake cubes, pudding, whipped topping, and the rest of the toffee bits, creating a visually appealing layered effect.

Cover the assembled dessert and place it in the refrigerator for a minimum of 1 hour, or up to 24 hours, to allow the layers to meld and flavors to intensify. Just before presenting, optionally adorn the top with chocolate curls or a sprinkle of extra toffee pieces.