500g icing sugar
250ml good quality cocoa powder
1 egg, slightly beaten
1tsp vanilla essence
1 packet Marie biscuits broken into pieces (bash in a packet or use a food processor)
Melt the butter in a large pot until melted. Remove from the heat and add the icing sugar and cocoa. Mix well until well combined and there are no dry bits. Stir in the beaten egg and vanilla and mix until smooth. Add the broken biscuit bits and stir until well combined and evenly coated with chocolate. Spoon the mixture into a greased 24 x 24 cm and smooth out with a spatula.
Once cooled and firm (pop into the fridge to speed up the process), cut into 16 squares and keep in an airtight container.