Line a cake tin with a circle of baking paper
Put the biscuits in a food processor and blitz until fine.
Melt the butter in a microwave. Add the biscuit crumbs into a bowl along with the butter and mix thoroughly. Pour the biscuit mix into the cake tin and flatten down with the back of a spoon. Put this in the freezer for 20 minutes.
Meanwhile whisk together the cream cheese, icing sugar and orange and zest until smooth. Add in the double cream and whisk on high until it is thick.
Melt the dark chocolate and fold through the cheesecake mixture.
Spread this into the cake tin on top of the biscuit base and flatten as well as you can. Pop this into the fridge for 5-6 hours to set (or freezer for 1-2 hours)
Once set, for the decoration melt some dark chocolate and white chocolate in the microwave. Add some orange food colouring into the white chocolate. Add this into piping bags and snip a teeny bit off the end. Drizzle in a criss cross pattern over the top of the cheesecake and finish off with chocolate orange pieces.
Store in the fridge and eat within 3 days.