01 - Preheat oven to 350°F. Grease a 9x13-inch baking pan with nonstick spray or butter.
02 - In a large mixing bowl, combine chocolate cake mix, eggs, water, and vegetable oil. Mix with an electric mixer on medium speed until the batter is smooth, following package guidelines.
03 - Pour batter into the prepared baking pan and bake for 28 to 32 minutes, or until a toothpick inserted in the center comes out clean.
04 - Allow the cake to cool for 10 to 15 minutes, letting it firm slightly while remaining warm.
05 - Using the handle of a wooden spoon, create holes evenly across the surface of the cake, spacing them about 1 inch apart.
06 - In a medium bowl, whisk together vanilla pudding mix, cold milk, peppermint extract, and food coloring if using, until thickened, about 2 minutes.
07 - Pour the prepared pudding evenly over the cake. Use a spatula to gently spread the pudding, pressing it into the holes so it soaks into the cake structure.
08 - Cover the cake with plastic wrap and refrigerate for at least 1 hour, or until the pudding layer is set.
09 - Spread the thawed whipped topping over the chilled cake in an even layer.
10 - Sprinkle the surface with crushed peppermint candies and optionally add chocolate shavings or mini chocolate chips.
11 - Cut the cake into slices and serve chilled.