Preheat oven to fan forced 180ºC. Line a 20cm square pan with baking paper ensuring edges along one side come up over the top of the pan for easy removal.
Place 50g macadamia nuts into Thermomix bowl and mill by pushing the Turbo button ONCE.
Add remaining base ingredients into Thermomix bowl and blend 7 sec/speed 6 until mixture resembles breadcrumbs.
Press into lined tin. Sprinkle most of the remaining roasted macadamia nuts over the top of base reserving a few for the topping later.
To make topping place butter, sugar and vanilla into Thermomix bowl and cook 4 min/80ºC/speed 1. Blend 8 sec/speed 8.
Pour mixture over base and bake for 20 minutes until caramel is bubbling.
While the slice is still hot, top with extra chopped macadamias and around 150g chopped chocolate. Allow the chocolate to melt slightly on the hot slice.
Leave to cool in tin and using very sharp knife, slice into squares when cold.