Preheat the oven to 180°C and grease a 23cm springform cake tin.
Slice a thin disc from the sponge flan case to fit the base of the tin and drizzle with 15ml of orange liqueur.
Mix sugar, orange zest, juice, and cornflour, then beat in the cream cheese and eggs until incorporated.
Incorporate the vanilla seeds, remaining orange liqueur, and cream until the mixture is completely smooth.
Layer a third of the mixture with a third of the chocolate pieces in the tin and repeat twice.
Bake in a water bath for 50 minutes until golden, then cool and set completely.
Melt white chocolate and dark chocolate in separate bowls over simmering water.
Pour both chocolates onto a cling-film covered tray, swirl with a finger to marble, and chill until set.
Serve cheesecake wedges with shards of marbled chocolate and a drizzle of cream.