Grease and line the base of a 20cm round cake tin with nonstick baking paper. Heat the oven to 150°C. Crush the bourbon biscuits to a fine crumb and mix with the toasted hazelnuts and butter. Press into the base and sides of the cake tin and put in the fridge to set. Meanwhile, place the cream cheese, caster sugar, vanilla and eggs in a mixer fitted with a whisk and beat together till smooth. Remove half of the mixture and put aside. Add the melted chocolate and cocoa to the mixer bowl and mix well. Spoon the chocolate cheesecake filling into the biscuit base. Break the white chocolate with hazelnuts into squares and press into the mixture. Carefully spread over the plain cheesecake mixture and flatten out. Bake in the oven at 150°C for approximately 55 minutes ( it should still feel wobbly in the middle) Allow to cool down in the oven with the door open for 20 minutes then place into the fridge to cool down completely. Place onto a serving dish, dust the top with extra cocoa powder, hazelnuts and fresh edible flowers.