Step 1: Bake the Chocolate Cake

1. Preheat your oven according to the cake mix instructions. Grease and flour a 9×13-inch baking pan.
2. In a large bowl, combine the chocolate cake mix, water, vegetable oil, and eggs. Mix until well combined.
3. Pour the batter into the prepared pan and bake according to the package instructions. Once baked, allow the cake to cool completely.

Step 2: Prepare the Chocolate Pudding

1. In a large bowl, whisk together the instant chocolate pudding mix and milk until smooth. Let it sit for about 5 minutes to thicken.

Step 3: Make the Whipped Cream

1. In a large mixing bowl, beat the heavy whipping cream, powdered sugar, and vanilla extract with an electric mixer until soft peaks form.

Step 4: Assemble the Trifle

1. Once the chocolate cake is completely cool, cut it into cubes.
2. In a large trifle dish or individual serving glasses, layer the ingredients as follows: start with chocolate cake cubes, then chocolate pudding, then whipped cream. Repeat the layers until all ingredients are used, finishing with whipped cream on top.

Step 5: Garnish and Chill

1. Top the final layer of whipped cream with chocolate shavings or curls, fresh berries, and mint leaves if desired.
2. Cover the trifle with plastic wrap and refrigerate for at least 2 hours (or overnight) to allow the flavors to meld.

Step 6: Serve

1. Scoop the trifle into individual bowls or serve directly from the trifle dish. Enjoy your festive dessert!