Bake the cake according to package directions using a 9x13-in. baking pan.
Just before the cake is finished baking, combine the sweetened condensed milk and peppermint extract in a small bowl. Set aside.
After baking, remove the cake from the oven and poke holes in the cake with the round end of a wooden spoon.
Carefully pour the sweetened condensed milk mixture over the cake, trying to fill the holes as much as possible. Then, allow the cake to cool completely.
Heat the hot fudge sauce just until it is spreadable, then evenly pour it over the top of the cake. If necessary, spread the hot fudge sauce with an offset spatula or the back of a spoon to ensure it is evenly over the cake. Allow the sauce to cool completely, about 15 minutes.
Spread the whipped topping evenly over the cake, then top with the peppermint crunch baking chips.
Refrigerate the cake for at least 4 hours before serving.
Notes
Feel free to use crushed candy canes in place of the Andes Peppermint Crunch Baking Chips.
You can use a white cake mix if you prefer.
If you prefer to use a homemade cake instead of a box mix, you totally can. Just be sure to bake it in a 9x13-in. baking dish.
For an extra touch of festivity, add some colorful holiday sprinkles to the top of the cake!