01 - Preheat oven to 350°F. Lightly grease a 9x13-inch baking pan.
02 - In a large bowl, blend chocolate cake mix, eggs, water, and vegetable oil until smooth using mixer or whisk.
03 - Pour batter into prepared pan. Bake for 28 to 32 minutes or until a toothpick comes out clean from the center.
04 - Let cake cool for 10 to 15 minutes. Using the handle of a wooden spoon, poke holes evenly over the surface, spacing about 1 inch apart.
05 - Whisk together instant vanilla pudding mix, cold milk, peppermint extract, and food coloring (if using) until thickened, about 2 minutes.
06 - Pour pudding mixture evenly over cooled cake, spreading and working it into holes with a spatula.
07 - Cover cake and chill in the refrigerator for at least 1 hour until pudding is set.
08 - Spread thawed whipped topping evenly across chilled cake surface.
09 - Sprinkle with crushed peppermint candies and chocolate shavings or mini chocolate chips if desired.
10 - Cut into pieces and serve cold.