01 - Preheat oven to 350°F. Lightly grease a 9x13-inch baking pan.
02 - In a large mixing bowl, blend cake mix, eggs, water, and vegetable oil until batter is smooth.
03 - Pour batter into prepared pan and bake for 28 to 32 minutes, or until a toothpick inserted in the center emerges clean.
04 - Set cake aside to cool for 10 to 15 minutes after baking.
05 - With the handle of a wooden spoon, evenly poke holes across the cake surface spaced about 1 inch apart.
06 - In a medium bowl, vigorously whisk instant vanilla pudding mix, cold milk, peppermint extract, and food coloring if using, until mixture thickens, about 2 minutes.
07 - Immediately spread pudding over the cake, allowing it to seep into the holes and smoothing the top with a spatula.
08 - Cover and refrigerate the cake for at least 1 hour or until fully set.
09 - Evenly spread thawed whipped topping over cake once chilled.
10 - Sprinkle crushed peppermint candies and chocolate shavings or chips on top. Slice and serve chilled.