Base: Grind the chocolate biscuits and chocolate in a food processor; the crumbs should be small. Mix in sugar. Melt butter and add it to the chocolate crumbs. Press into the bottom of a 22cm springform pan.
Filling: Melt chocolate and cool slightly. Blend in cream cheese, sugar, eggs, cream, cocoa, vanilla and peppermint essence. Pour this in crust. Bake for one hour at 180 degrees C. Cool overnight.
Topping: In a small bowl mix together the sour cream and sugar. Pour on top of cooled cheesecake. Bake for 20 minutes at 180 degrees C. Chill for 6 to 8 hours.
Chocolate Icing: In a small saucepan simmer cream and butter. Add to this the chocolate and stir until melted. Remove from heat. Freeze until the mixture is piping consistency. Using a pastry bag pipe a lattice on the top.