01 - Preheat the 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. Mix using an electric mixer or whisk until a smooth batter forms, following the manufacturer's instructions on the cake mix package.
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 - Transfer the baked cake to a wire rack and 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 using) until slightly thickened, about 2 minutes.
07 - Quickly pour the pudding over the cake, spreading evenly with a spatula so the pudding fills the holes.
08 - Cover and refrigerate for at least 1 hour until the pudding is set.
09 - Spread the thawed whipped topping evenly across the surface of the chilled cake.
10 - Sprinkle crushed peppermint candies and chocolate shavings or mini chocolate chips over the whipped topping.
11 - Cut into portions and serve chilled.