Keep the butter out of the fridge a few hours before you start. It's very important that the butter is super soft (but not melted) so it will make a smooth batter. Prepare a cup of strong espresso and let it cool down.
Add the butter, powdered sugar and two egg yolks (keep the egg whites aside, to use later). Mix it with a wooden spoon until smooth.
Beat the egg whites firm. Add the egg white gently bit by bit to the batter and fold it. Don't beat it, it needs to stay light and fluffy.
Prepare a cake tin with parchment paper and grease it with a bit of butter. Dip the biscuits one by one in the coffee and create the first layer ( make sure the coffee is cold, otherwise the biscuits will break). Add a layer of cream on top and repeat until there is no biscuits and cream left and you created an even layer on top. Finish with cocoa powder and if you like you can add chocolate sprinkles or chocolate shavings. Put the cake tin in the fridge and let it harden overnight, or at least 6/8 hours. The more, the better!
Serve as a desert or with coffee. Bon appétit!