01 - Preheat oven to 350°F. Grease a 9x13-inch baking pan with non-stick spray or butter.
02 - In a large mixing bowl, combine chocolate cake mix, eggs, water, and vegetable oil. Blend with an electric mixer or whisk until batter is smooth.
03 - Pour batter evenly into prepared pan. Bake for 28 to 32 minutes, or until a toothpick inserted into the center comes out clean.
04 - Remove cake from oven and allow it to cool in the pan for 10 to 15 minutes.
05 - Using the handle of a wooden spoon, create holes over the surface of the cake, spacing them about 1 inch apart.
06 - In a medium bowl, whisk instant vanilla pudding mix, cold milk, peppermint extract, and food coloring (if using) for about 2 minutes until thickened.
07 - Immediately pour and spread the pudding mixture evenly over the cake, ensuring it fills the holes. Use a spatula to gently assist.
08 - Cover the cake and refrigerate for at least 1 hour, or until the pudding is set.
09 - Spread thawed whipped topping smoothly across the surface of the chilled cake.
10 - Sprinkle crushed peppermint candies and chocolate shavings or mini chocolate chips over the topping as desired.
11 - Cut into portions and serve while chilled.