01 - Preheat oven to 350°F. Lightly grease a 9x13-inch baking pan.
02 - Combine chocolate cake mix, eggs, water, and oil in a large mixing bowl. Beat with an electric mixer or whisk until smooth and fully blended.
03 - Pour batter into prepared pan. Bake for 28 to 32 minutes, or until a toothpick inserted in the center emerges clean.
04 - Allow cake to cool in the pan for 10 to 15 minutes. Using the handle of a wooden spoon, create holes across the cake surface, spaced about 1 inch apart.
05 - In a medium bowl, vigorously whisk together instant vanilla pudding mix, cold milk, peppermint extract, and food coloring (if using) until thickened, about 2 minutes.
06 - Immediately pour prepared pudding over the slightly cooled cake, spreading evenly and gently pressing the mixture into the holes using a spatula.
07 - Cover cake and refrigerate for at least 1 hour, or until pudding is set and the dessert is thoroughly chilled.
08 - Once chilled, spread thawed whipped topping evenly over the cake surface.
09 - Scatter crushed peppermint candies and chocolate shavings or mini chocolate chips across the whipped topping.
10 - Slice into servings and offer chilled.