Line an 8" square tin.
Start by crushing the biscuits. You could use a rolling pin or food processor. Add in the melted butter, melted chocolate, cocoa powder and sugar and stir to combine. Press into the lined tin and put in the fridge whilst making the filling.
Make the filling by combining the icing sugar, peppermint extract, green colour (just a drop, then add until you reach your desired shade) and about 80-90ml hot water. Stir together in a deep bowl (to avoid mess). The mixture should be thick but *just* spreadable. If too thick, add more water, a teaspoon at a time!
Spread over the base and set aside.
Melt the chocolate in a bowl in the microwave, in 20 second intervals. Pour over the mint layer and spread evenly. Place this in the fridge for at least an hour to totally set. Then, remove, let sit for 10 mins before slicing! (See notes for more tips on clean slices).
