01 - Preheat oven to 350°F. Grease a 9x13-inch baking pan.
02 - In a large bowl, combine chocolate cake mix, eggs, water, and vegetable oil. Beat with an electric mixer or whisk according to package instructions until batter is smooth.
03 - Pour batter into prepared pan. Bake for 28 to 32 minutes, or until a toothpick inserted into the center emerges clean.
04 - Allow cake to cool in pan for 10 to 15 minutes.
05 - With the handle of a wooden spoon, poke holes across the surface of the cake, about 1 inch apart.
06 - In a medium bowl, whisk instant vanilla pudding mix, cold milk, peppermint extract, and food coloring until thickened, about 2 minutes.
07 - Pour pudding evenly over cooled cake, spreading with a spatula to ensure pudding flows into holes.
08 - Cover and refrigerate for at least 1 hour, until pudding is set.
09 - Spread thawed whipped topping evenly over chilled cake.
10 - Sprinkle crushed peppermint candies and chocolate shavings or mini chocolate chips if desired. Cut into portions and serve chilled.