Grease and line a 18cm x 22cm rectangular slice tin with baking paper and set aside.
Place the Caramilk chocolate, butter and golden syrup into the Thermomix bowl. Melt for 3 minutes, 60 degrees, Speed 2.
Add the Rice Bubbles and mix for 15 seconds, Reverse, Speed 2, or until completely combined.
Press mixture very firmly into the prepared tin. Use a round glass or jug to press the mixture down as hard as you can (you'll hear some of the rice bubbles crushing).
Place the Caramilk chocolate and coconut oil into a clean Thermomix bowl. Melt for 3 minutes, 50 degrees, Speed 3 or until melted (scraping down the sides of the bowl occasionally).
Spread over slice and refrigerate until firm (a minimum of 3-4 hours - or best overnight).
Remove slice from the refrigerator about 30 minutes before cutting into squares with a warm serrated knife.