Let the butter melt very slowly on low heat. Break all the biscuits in small pieces. Line a cake tin with baking paper.
Mix the eggs and sugar together. Carefully add the cocoa powder through a sieve into the egg/sugar mixture. Pour in the melted butter. Do this one step at the time to make it easier to incorporate the butter into the mix. As soon as the butter is entirely incorporated into the mix add the biscuits and stir everything together so all biscuit pieces are coated with chocolate. Put everything in the cake tin
Put in the fridge and leave to stand at least 4 hours or preferably overnight to become solid enough to cut.