Crush/ break the biscuits into small pieces. Place them in a large bowl. if you are using nuts, crush them as well and add to the bowl. set aside.
In a saucepan combined sugar, butter, cocoa powder and water/coffee. Place the saucepan over medium heat and bring to a boil. Cook for 5-6 minutes, stirring constantly.
Pour chocolate syrup over the biscuits and stir until well coated.
Transfer the mixture into a 9-inch (23cm) pan. Press firmly to create flat surface cake. Refrigerate while making the ganache.
Make chocolate ganache: chop the chocolate and place in a heatproof bowl. In a small saucepan heat the cream, when starts to simmer remove from heat and pour over the chocolate. Let sit for 1-2 minutes and stir until melted and smooth.
Pour the ganache over the cake and refrigerate for at least 2-3 hours before serving.