01 - Preheat oven to 350°F. Lightly grease a 9x13-inch baking pan.
02 - Combine chocolate cake mix, eggs, water, and vegetable oil in a large bowl. Beat using an electric mixer or whisk until the batter is smooth, following box directions.
03 - Pour batter into prepared pan. Bake for 28 to 32 minutes, or until a toothpick inserted in the center comes out clean.
04 - Remove from oven and allow cake to cool for 10 to 15 minutes.
05 - Using the handle of a wooden spoon, create holes all over the surface at 1-inch intervals.
06 - In a medium bowl, whisk instant vanilla pudding mix, cold milk, peppermint extract, and food coloring until thickened, about 2 minutes.
07 - Immediately pour pudding over cake. Use a spatula to gently press and spread pudding into the holes and across the surface.
08 - Cover pan and refrigerate for at least 1 hour to fully set.
09 - Once chilled, evenly spread thawed whipped topping over the pudding layer.
10 - Sprinkle crushed peppermint candies and chocolate shavings or chips on top.
11 - Cut into squares and serve chilled.