Preheat oven to 160 degrees celsius (fan-forced). Line a muffin tray with cupcake liners and set aside.
Place the butter into the Thermomix bowl. Melt on 80 degrees, Speed 2, 2 minutes. Add the biscuits and mix on Speed 8, 10 seconds. Scrape down the sides and repeat until combined.
Divide the mixture between the cupcake liners and press down. Bake for 5 minutes. Set aside.
Place the cream cheese into a clean Thermomix bowl. Mix on Speed 4, 20 seconds.
Add the sour cream, caster sugar, vanilla extract, eggs and melted chocolate and mix on Reverse, Speed 3, 20 seconds.
Chop the Mars bars into small chunks and fold through the cream cheese mixture.
Divide the mixture between the prepared muffin holes (filling almost to the top).
Bake for 20 minutes or until just cooked.Allow to cool completely.
Decorate with extra chopped Mars bars and drizzle with chocolate sauce.
Store in an airtight container in the refrigerator for 3-4 days.