Preheat your oven to 350°F (175°C) and grease a 9×13 inch baking dish.

In a large mixing bowl, combine your chocolate cake mix according to the instructions on the box, using the required water, oil, and eggs. Mix until smooth.

Pour the batter into the prepared baking dish.

Bake in the preheated oven for 25-30 minutes, or until a toothpick inserted into the center comes out clean.

Allow the cake to cool for about 10 minutes.

Once cooled, use the handle of a wooden spoon or a fork to gently poke holes all over the cake—about 1 inch apart.

In a bowl, combine the sweetened condensed milk and chocolate syrup. Pour this mix over the poked cake, allowing it to seep into the holes and saturate the cake.

Cover the cake with plastic wrap and refrigerate for at least 2 hours, or overnight for best results.

Spread the whipped topping over the chilled cake. If desired, add chocolate shavings or sprinkles on top for decoration.

Slice and serve!