Line the base of a 22cm springform tin with baking paper and lightly grease the sides and finely chop two Mars Bars into pieces – set aside until needed.
Cut the butter in half and place into your Thermomix bowl. Cook for 2 minutes, 60 degrees, Speed 3 or until melted.
Add the Oreo (or chocolate ripple) biscuits and mix for 10 seconds, Speed 9. Use your spatula to scrape down the sides and mix again for another 10 seconds, Speed 7.
Pour the biscuit mixture into your prepared tin and use a large metal spoon to cover the base with the biscuit mixture and flatten the surface.
Cut four of the Mars Bars into quarters and place them into a clean Thermomix bowl. Chop them for 10 seconds, Speed 7 before cooking them for 3 minutes, 60 degrees, Speed 2 or until melted.
Add the vanilla extract, cream cheese, cream and caster sugar to the Thermomix bowl and mix for 30 seconds, Speed 5. Scrape down the sides and mix for another 30 seconds, speed 5.
Add ONE of the reserved chopped Mars Bars to the Thermomix bowl and mix for 20 seconds, REVERSE, Speed 2.
Pour the cheesecake mixture over the biscuit base and top with the remaining reserved Mars Bar pieces.
Place in the fridge to set for a minimum of eight hours, preferably overnight.