Grease and line a 20cm springform cake pan with baking paper.
Place 250g (or just over 1 full packet) of Tim Tams into a food processor and blitz until fine crumbs.
Add the melted butter to the biscuits and continue to process for another 15 seconds. Press the crumbs into the prepared pan and refrigerate while preparing the cheesecake mixture.
In the bowl of an electric mixer add the cream cheese, sugar and vanilla extract. Mix until smooth, then add the cream and continue to mix for another 1 minute.
In a small bowl, add ¼ cup cold water and sprinkle gelatine powder on top. Whisk with a fork and let it stand for 1 minute. Melt in the microwave in 20 second bursts to dissolve. Allow to cool slightly then add to the cheesecake batter in the electric mixer and mix for a further 30 seconds.
Add the cooled white chocolate and process for a further 30 seconds.
Chop up the remaining Tim Tams. Set aside ½ cup to decorate the top and stir the remaining biscuits into the cheesecake mixture by hand.
Pour the mixture over the base and refrigerate for a minimum of 4 hours or overnight.
To serve: decorate the top of the cheesecake with the reserved chopped Tim Tams.