In a large mixing bowl, combine the prepared chocolate pudding and whipped topping. Gently fold the whipped topping into the pudding until well blended and smooth.
In a trifle dish or a large glass bowl, layer half of the crumbled chocolate cake on the bottom.
Spread half of the chocolate pudding mixture over the cake layer.
Sprinkle half of the crushed toffee candy bars over the pudding layer.
Add a layer of mini chocolate chips and, if using, chopped nuts.
Repeat the layers with the remaining chocolate cake, pudding mixture, toffee, chocolate chips, and nuts.
Finish with a dollop of whipped topping on top and a sprinkle of mini chocolate chips and crushed toffee for garnish.
Cover the trifle with plastic wrap and refrigerate for at least 2 hours before serving to allow the flavors to meld.