Bake the chocolate cake mix according to the package instructions, using a greased 9x13-inch pan. Allow the cake to cool completely on a wire rack for about 30 minutes, then cut into 1-inch cubes.

In a medium-sized bowl, whisk together the instant chocolate pudding mix with 2 cups of cold milk for about 2 minutes until it thickens and becomes smooth. Allow the pudding to chill for a few minutes.

Layer half of the chocolate cake cubes in a trifle dish, followed by half of the pudding mixture, then half of the whipped topping, and half of the crushed toffee bits.

Repeat the layers with the remaining cake cubes, pudding, whipped topping, and crushed toffee bits.

Cover the trifle with plastic wrap and refrigerate for at least 1 hour to chill and meld the flavors.

When ready to serve, remove the trifle from the refrigerator and garnish with additional toffee bits or chocolate curls.