01 - Preheat oven to 350°F and lightly grease a 9x13-inch baking pan.
02 - In a large mixing bowl, blend chocolate cake mix, eggs, water, and oil following package instructions until the batter is smooth.
03 - Transfer batter to 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 in the pan.
05 - Using the handle of a wooden spoon, poke holes across the entire surface of the cake, spacing about 1 inch apart.
06 - In a medium bowl, whisk instant vanilla pudding mix, cold milk, peppermint extract, and food coloring, if desired, until thickened (approximately 2 minutes).
07 - Immediately pour pudding evenly over cooled cake, using a spatula to spread and press pudding into holes.
08 - Cover and refrigerate for at least 1 hour until set.
09 - Spread thawed whipped topping evenly over chilled cake.
10 - Sprinkle with crushed peppermint candies and, if desired, chocolate shavings or mini chocolate chips.
11 - Slice and serve cold.