Crush the biscuits to a fine crumb
Melt the margarine and pour into the crushed biscuits. Mix well and then press into the base of the cake tin
Drizzle the espresso over the biscuit base
Whisk together the cream cheese, icing sugar and vanilla (if using) until nice and smooth
Spread over the top of the biscuit base. I like to make a swirl type pattern on top to make the the cocoa look more dramatic
Dust with the cocoa powder and then place in the fridge to firm up (or serve staright away if you can't wait!)