Place the butter, sweetened condensed milk and vanilla extract into the Thermomix bowl and melt on Speed 2, 80 degrees, 2-3 minutes (or until melted).
Add the biscuits and coconut and mix on Speed 6, 5 seconds. Scrape down the sides of the bowl and repeat for a further 5 seconds of until combined.
Place the mixture into the prepared slice tin and push down firmly with the back of a spoon. Place into the fridge.
In a clean and dry Thermomix bowl, melt the milk chocolate and coconut oil on Speed 2, 60 degrees, 2-3 minutes, or until melted.
Once melted, pour over the slice and sprinkle with extra coconut (if desired).
Place back into the fridge to set.