Start by lining the base and sides of a square or rectangular cake tin with cling film or baking paper. Place the double cream into a medium sized pan and heat till almost boiling. Remove off the heat, add in the chopped chocolate and allow to melt. Mix together well before stirring in the liqueur of your choice. Next, soak the biscuits in the cold coffee, one by one and place into the bottom of the tin or dish. Spread over a little of the ganache. Repeat the process 4 or 5 times till you have used up all the ingredients, dust the top with coca powder and chill for 2-3 hours until completely set.