Preheat the oven to 160°C and grease a 20cm cake tin.
Mix the crushed biscuits and melted butter then press into the tin.
Melt the chocolate in a bowl over hot water and allow to cool slightly.
Beat the cheese until soft then mix in the sugar, vanilla, and eggs individually.
Spoon half the plain mixture into the tin as separate dollops.
Combine melted chocolate with the remaining cheese mixture and fill the gaps.
Swirl the surface to create a marbled effect.
Bake for 30 minutes until puffy at the edges but soft in the centre.
Switch off the oven and leave the cake inside to cool completely.
Chill thoroughly before loosening from the tin to serve.