Warm up the milk and add cocoa powder and sugar.

Mix it together and boil the cocoa mixture. Set it aside for 20 minutes to cool.

Take your pre-made spongecake and slice it in half.

(You can also use ladyfingers if you don't have a spongecake made.)

Have a cake pan ready. You can either use the same cake pan you used for baking your spongecake, or if you're using ladyfingers, use a rectangular glass container for easier layout.

Soak the spongecake or the ladyfingers in the earlier prepared chocolate milk.

Using a wide spatula, take half of the mousse portion and spread it on the soaked portion of the spongecake (ladyfingers).

Soak the other half of the spongecake with cocoa and place it on top. If you're using ladyfingers, soak them and line them up on top.

Take the remaining portion of the mousse and spread it on top.

Cover it with aluminum foil and refrigerate the cake for at least 2 hours before serving. For best results, leave it in the fridge overnight.