Oil a 23cm spring-clip tin and line the base with parchment.
Melt the dark chocolate in a bowl over simmering water and let cool.
Blitz the biscuits into crumbs using a food processor.
Blend the crumbs with melted butter.
Press the mixture firmly into the base of the prepared tin.
Freeze the base until hardened.
Preheat the oven to 180°C.
Blend the cheese, cream, sugar, and eggs until smooth, then incorporate melted chocolate.
Wrap the tin base in foil and place inside a roasting tin.
Pour the filling over the base and add hot water to the roasting tin halfway up the sides.
Bake in the center of the oven for 35 to 45 minutes until slightly wobbly.
Cool in the oven with the door ajar for 1 hour, then chill for 4 hours.
Remove the cheesecake from the tin and place on a serving plate.
Decorate with chocolate truffles and grated white chocolate.