01 - Preheat oven to 350°F. Grease a 9x13-inch baking pan.
02 - In a large mixing bowl, combine chocolate cake mix, eggs, water, and oil. Beat according to package directions until 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 cake to cool in the pan for 10 to 15 minutes.
05 - Using the handle of a wooden spoon, poke holes evenly over the cake, spacing about 1 inch apart.
06 - In a medium bowl, whisk together instant pudding mix, cold milk, peppermint extract, and food coloring, if using, until thickened, about 2 minutes.
07 - Immediately pour pudding over cake, gently spreading and pressing it into holes with a spatula.
08 - Cover and refrigerate cake 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 chocolate chips, if using.
11 - Slice and serve cold.