01 - Preheat the oven to 350°F. Lightly grease a 9x13-inch baking pan with nonstick spray.
02 - In a large mixing bowl, combine the chocolate cake mix, eggs, water, and vegetable oil. Mix with an electric mixer or whisk until batter is smooth and combined.
03 - Pour batter into the prepared baking pan, smoothing the top. Bake for 28 to 32 minutes, or until a toothpick inserted in the center comes out clean.
04 - Remove cake from the oven and let cool in the pan for 10 to 15 minutes.
05 - With the handle of a wooden spoon, poke holes evenly across the cake surface, spaced about 1 inch apart.
06 - In a medium bowl, whisk together instant vanilla pudding mix, cold milk, peppermint extract, and food coloring if using, until thickened, about 2 minutes.
07 - Pour the pudding evenly over the cake, using a spatula to spread and gently push filling into the holes.
08 - Cover pan and refrigerate for at least 1 hour, or until pudding is set.
09 - Spread thawed whipped topping evenly over the chilled cake.
10 - Sprinkle crushed peppermint candies over the surface and add chocolate shavings or chips if desired.
11 - Slice and serve the dessert chilled.