Preheat your oven to 350°F (175°C). Grease a 9×13 inch baking pan.

In a large mixing bowl, combine the chocolate cake mix, water, vegetable oil, and eggs. Mix until well blended, about 2 minutes.

Pour the batter into the greased pan and bake according to the package instructions, typically around 30-35 minutes. A toothpick inserted into the center should come out clean.

Once baked, remove the cake from the oven and allow it to cool for about 10 minutes. Using the handle of a wooden spoon or a fork, poke holes all over the top of the cake, about 1 inch apart.

In a separate bowl, mix together the sweetened condensed milk and chocolate fudge sauce. Pour this mixture evenly over the entire surface of the cake, letting it seep into the holes you made.

Allow the cake to cool completely in the pan. Once it’s cooled, spread the whipped topping over the top, covering it completely.

Finish with chocolate shavings or sprinkles if desired. Cover and refrigerate the cake for at least 2 hours before serving, allowing the flavors to meld together.