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 vegetable oil. Blend with an electric mixer or whisk until smooth.
03 - Pour the batter into the prepared pan. Bake for 28 to 32 minutes, or until a toothpick inserted in the center comes out clean.
04 - Remove from oven and allow cake to cool for 10 to 15 minutes.
05 - Using the handle of a wooden spoon, poke holes evenly across the cake surface, spacing about 1 inch apart.
06 - In a medium bowl, whisk together instant pudding mix, cold milk, peppermint extract, and food coloring if desired, mixing until the pudding thickens, about 2 minutes.
07 - Evenly pour the pudding over the cooled cake. Use a spatula to spread and encourage the pudding into the holes. Cover and refrigerate for at least 1 hour until set.
08 - Spread thawed whipped topping evenly over the chilled cake.
09 - Sprinkle with crushed peppermint candies and chocolate shavings or mini chocolate chips if desired. Slice and serve chilled.