Garnish with chocolate shavings or chocolate curls. To make the curls, pull a vegetable peeler across a milk chocolate candy bar, using long, thin strokes. (The curls will be easier to make if the chocolate is slightly warm, so let the chocolate stand in a warm place for about 10 minutes.) Use a toothpick to lift the curls from the chocolate to the trifle.
Drizzle the whipped topping mixture with additional caramel topping and sprinkle with additional chopped walnuts.