Grease and line an 18cm x 28cm rectangular baking tin with baking paper and set aside.
Place the butter into the Thermomix bowl and melt for 3 minutes, 80 degrees, Speed 2.Add the biscuits and mix for 8 seconds, Speed 8. Scrape down the sides of the bowl and repeat until combined. Press the biscuit base firmly into the prepared baking tin.
In a clean and dry Thermomix bowl, whip the cream on Speed 3 with the MC lid removed (the time taken will depend on the freshness of the cream - it can be anywhere from 10 seconds to a couple of minutes!) Set the whipped cream aside in a separate bowl.
Mix the softened cream cheese and the caster sugar for 10 seconds, Speed 5. Scrape down the sides of the bowl and repeat until smooth and creamy.
In a separate bowl, sprinkle the gelatine over the boiling water and stir until completely dissolved.
Add the gelatine mixture through the cream cheese mixture and mix for 10 seconds, Speed 4.
Add 150g of the salted caramel sauce and mix for 10 seconds, Speed 4.Note: if you want to add the caramel swirls at the end to decorate, set aside ¼ and only beat through ¾ of the caramel sauce in this step. Fold through the whipped cream with the spatula.
Pour the cream cheese mixture over the biscuit base.
Optional: Swirl the remaining warm salted caramel sauce through the top of the cheesecake (using a skewer or a knife).
Place into the fridge for 6 hours or until completely set.
Cut into slices and serve.