01 - Preheat oven to 350°F. Grease a 9x13-inch baking pan thoroughly.
02 - In a large mixing bowl, combine chocolate cake mix, eggs, water, and vegetable oil. Blend using an electric mixer or whisk until the mixture is smooth and homogeneous.
03 - Transfer batter to the prepared pan. Bake for 28 to 32 minutes, or until a toothpick inserted in the center emerges clean.
04 - Allow cake to cool for 10 to 15 minutes. Using the handle of a wooden spoon, create evenly spaced holes across the surface, approximately 1 inch apart.
05 - In a medium bowl, whisk together instant vanilla pudding mix, cold milk, peppermint extract, and food coloring if using. Whisk for about 2 minutes until thickened.
06 - Immediately pour prepared pudding over the cooled cake, spreading it gently and pressing pudding into each hole with a spatula.
07 - Cover and refrigerate for at least 1 hour, or until the pudding is set throughout.
08 - Spread thawed whipped topping evenly over the chilled cake.
09 - Sprinkle crushed peppermint candies and chocolate shavings or mini chocolate chips over the surface.
10 - Cut cake into pieces and serve chilled for optimal texture and flavor.