01 - Preheat oven to 350°F. Grease a 9x13-inch baking pan.
02 - In a large bowl, blend chocolate cake mix, eggs, water, and vegetable oil using an electric mixer or hand whisk until smooth and homogenous.
03 - Transfer batter into prepared pan and bake for 28–32 minutes or until a toothpick inserted in the center emerges clean.
04 - Allow cake to cool in the pan for 10–15 minutes to prevent excess crumbling.
05 - With the handle of a wooden spoon, poke holes uniformly across the cake surface at 1-inch intervals.
06 - In a medium bowl, whisk together instant vanilla pudding mix, cold milk, peppermint extract, and food coloring if desired, until thickened, approximately 2 minutes.
07 - Evenly pour the peppermint pudding over the cooled cake, gently spreading and pressing the mixture into the holes with a spatula.
08 - Cover cake and refrigerate for a minimum of 1 hour or until pudding layer is fully set.
09 - Spread thawed whipped topping over the chilled cake in an even layer.
10 - Sprinkle crushed peppermint candies and chocolate shavings or chips on top as desired.
11 - Slice cake and serve chilled for optimal texture and flavor.