Preheat the oven according to the box cake mix instructions. Prepare a 9x13-inch cake pan with cooking spray. Set aside.
Prepare the chocolate cake mix using the required ingredients as directed on the back of the box. Usually calls for oil, water, and eggs.
1 box (15.25 oz) chocolate cake mix, ingredients for the cake mix
Pour the chocolate cake batter into the prepared pan. Bake according to the box instructions (usually around 20-30 minutes). A toothpick inserted into the center should come out clean.
Remove the cake from the oven and let it cool for 10 minutes.
Use the handle of a wooden spoon or a straw, and poke holes all over the surface of the cake, about 1-inch apart.
In a medium bowl, whisk together the instant chocolate pudding mix, milk, and peppermint extract until smooth and thickened (if it's not thickening, allow it to sit for a few minutes to thicken up).
1 box (3.9 oz) instant chocolate pudding mix, 2 cups whole milk, ½ teaspoon peppermint extract
Pour the pudding mixture over the cake, ensuring it fills each hole. Spread it out evenly with a rubber spatula.
Let the cake cool completely at room temperature, then cover the cake with a lid or plastic wrap, and refrigerate it for 2-4 hours or up to overnight.
Add the heavy whipping cream, powdered sugar, and vanilla extract into a mixing bowl. Beat with an electric hand mixer or a stand mixer, until stiff peaks form. Spread the homemade whipped cream evenly over the chilled cake.
2 cups heavy whipping cream, 6 tablespoons powdered sugar, 1 teaspoon vanilla extract
Sprinkle the crushed peppermint candies evenly over the top of the whipped cream. Serve & enjoy!*If you want the whipped cream chilled with the cake before serving (I prefer doing it this way), leave the peppermint candies off, cover the cake with a lid or plastic wrap and refrigerate for up to 4-6 hours before serving. Add the crushed candies on right before serving. finely crushed peppermint candy canes