Prepare cake mix according to directions on box, using the eggs, oil, and buttermilk or milk.
Grease a 13x9 pan and pour batter in. Bake your cake according to directions on the box. Cool completely.
Meanwhile, whisk together pudding and milk until smooth in a large bowl and place in the refrigerator to set.
To assemble trifles, layer cake, pudding, and whipped topping.
Top with garnish if you like.
Serve immediately or place in refrigerator until ready to serve.
Should be served the same day.
Notes
Flavor variation: You can switch up the flavor of your chocolate pudding trifle cups by using different types of pudding mixes, including vanilla, chocolate, pistachio, and even cheesecake flavored pudding.