Grease and line the base and sides of a 20cm springform pan with baking paper and set aside.
Melt the butter in a clean Thermomix bowl for 2 minutes, 90 degrees, Speed 2 (or until completely melted).
Add the Oreos/biscuits and mix for 5 seconds, Speed 9, or until fine crumbs remain.
Press into the base of the prepared tin and set aside.
Whip cream in a clean, dry Thermomix bowl on Speed 3.5 until lightly whipped (the time it takes will depend on the freshness of the cream - it can be anywhere between 10 seconds and 2 minutes!!) Set the cream aside in a separate bowl.
Place the white chocolate into the Thermomix bowl and melt for 3 minutes on 50 degrees, Speed 2. Set aside in a bowl to cool slightly.
Beat the cream cheese, vanilla extract and caster sugar in a clean and dry Thermomix bowl for 30 seconds, Speed 5. Scrape down the sides with a spatula and repeat until smooth and creamy.
Place the boiling water into a small bowl and sprinkle over the gelatine powder (1 tsp at a time). Use a fork to whisk until completely dissolved and allow to cool slightly.Pour the cooled gelatine mixture into the Thermomix bowl and mix for 20 seconds, Speed 4, or until completely combined.
Gently fold through the whipped cream, melted white chocolate, and chopped Mars Bars with the spatula.
Pour the mixture into the prepared tin and spread out evenly.
Chill in the fridge for at least 6 hours (preferably overnight).
When ready to serve, decorate with caramel sauce and the extra chopped Mars Bars.