01 - Preheat oven to 350°F. Grease a 9x13-inch baking pan.
02 - Combine chocolate cake mix, eggs, water, and vegetable oil in a large bowl. Mix thoroughly following package directions until batter is smooth.
03 - Pour batter into prepared pan. Bake for 28 to 32 minutes, or until a toothpick inserted in the center emerges clean.
04 - Allow to cool for 10 to 15 minutes on a wire rack.
05 - Using the handle of a wooden spoon, create evenly spaced holes across the cake surface about 1 inch apart.
06 - In a medium bowl, whisk instant vanilla pudding mix, cold milk, peppermint extract, and food coloring, if using, until thickened, approximately 2 minutes.
07 - Pour and gently spread pudding mixture over the cake, ensuring even distribution and pressing pudding into holes with a spatula.
08 - Cover and refrigerate for at least 1 hour, or until pudding is set.
09 - Spread thawed whipped topping evenly over chilled cake.
10 - Sprinkle with crushed peppermint candies and chocolate shavings or mini chips, if desired.
11 - Slice and present chilled.