In a food processor, blend the biscuits to a fine crumb. Stream in the butter, and process until mixture comes together. Press into 6 jars, and place in the fridge for a minimum 30 minutes.
In a bowl, beat together the Tatua Mascarpone, caster sugar, ½ cup Nutella and vanilla. Fold in whipped cream, then spoon onto the biscuit bases. Melt the remaining Nutella in the microwave for 30 seconds, then pour over the top of the cheesecake mixture. Place in the fridge to set for 3 hours or overnight.
Garnish cheesecakes with chopped hazelnuts and hazelnut chocolates if desired, and serve.