Blitz the biscuits to a fine crumb - I used a food processor to do this, but you can use a large bowl with the end of a rolling pin.
Add the cocoa powder, and mix to combine.
Add the melted butter, and mix to a wet sand texture - press into the bottom of a deep 8"/20cm deep springform cake tin.
Add the full-fat soft cream cheese to a large bowl, and add the icing sugar and the peppermint extract.
Whisk the mixture together until smooth.
Pour in the double cream and whisk the mixture together until thick - or, you can whip the cream to firm peaks in a separate bowl, and then fold the two mixtures together.
Spread the cheesecake mixture onto the biscuit base, making sure to pack it into the sides of the tin to prevent air gaps.
Set the cheesecake in the fridge for a minimum of 6 hours, but preferably overnight.
Once the cheesecake has set, carefully remove it from the tin.
If you need to, you can smooth the sides of the tin with a small knife or palette knife.
Add the milk chocolate, dark chocolate and double cream to a jug/bowl and heat in the microwave on a low heat until smooth. It's best to do this in short bursts such as 20-30 seconds, stirring well each time so you don't accidentally overheat the mixture.
Once melted, let the ganache cool for a minute or two.
Carefully pour the ganache onto the cheesecake, and carefully push it over the edges of the cheesecake to create the drip.
Let the cheesecake set for 10 minutes in the fridge.
Add the double cream and icing sugar to a bowl, and whisk to soft peaks and pipeable.
Pipe onto the cheesecake to decorate - I used a 2d closed star piping tip.