01 - Preheat oven to 350°F. Grease a 9x13-inch baking pan.
02 - In a large bowl, blend chocolate cake mix, eggs, water, and vegetable oil as directed on the package until smooth. Pour batter into prepared pan and bake for 28–32 minutes or until a toothpick inserted in the center comes out clean.
03 - Remove cake from oven and let cool for 10–15 minutes. Using the handle of a wooden spoon, poke holes across surface spaced about 1 inch apart.
04 - In a medium bowl, whisk instant pudding mix, cold milk, peppermint extract, and food coloring (if using) for about 2 minutes until thickened. Immediately pour pudding evenly over the cake, spreading and gently pressing pudding into the holes with a spatula.
05 - Cover cake and refrigerate for at least 1 hour until pudding is set.
06 - Spread thawed whipped topping evenly over the chilled cake surface.
07 - Sprinkle with crushed peppermint candies and chocolate shavings or mini chocolate chips as desired.
08 - Cut into portions and serve chilled.