Preheat oven to 170°C and grease a 20cm springform tin with butter and parchment.
Melt butter and plain chocolate in a saucepan and stir in crushed biscuits.
Press the mixture into the tin base and chill in the fridge.
Melt white chocolate in a bowl over simmering water until smooth.
Whisk cream cheese, soured cream, eggs, and vanilla, then stir in melted chocolate and ginger.
Pour filling over the base and bake for 40-45 minutes until set.
Rest for 10 minutes, loosen edges with a knife, and chill until cold.
Pipe eleven chocolate holly leaf shapes onto parchment strips using melted chocolate.
Curve the parchment over rolling pins and let the chocolate leaves set.
Knead red food colouring into marzipan and roll into 27 small berry balls.
Remove the cheesecake from the tin and place it on a serving plate.
Whip double cream to soft peaks and pipe nine rosettes onto the cheesecake.
Garnish the cream rosettes with chocolate holly leaves and marzipan berries.