Place biscuits in a large bag and crush them using a rolling pin.
Mix soft butter, cocoa powder, sugar and egg in a bowl.
Add biscuit crumbs and mix until combined.
Spread the mixture out on a plastic wrap and shape it into a log. Roll up and place the salami for at least 3 hours in the fridge.
Remove the plastic wrap and dust with icing sugar from all sides. Cut into pieces and serve. Keep the salami in the fridge and take it out before serving.