To begin, line the base and sides of a slice tin with baking paper - making sure you leave the paper hanging over the edges.
Place the marshmallows and butter into the thermomix bowl and cook for 1 minute on 80 degrees, speed 1 or until melted and combined. After approximately 30 seconds, use the spatula to scrape down the sides.
Add the rice bubbles to the bowl and mix for 1 minute 20 seconds on speed 1 Reverse until mixture has combined.
Pour the combined mixture into a slice tin and use a metal spoon to spread across the
tin and push down.
If decorating, sprinkle the 100s and 1000s over the top of the slice and place in the fridge for two hours or until set.
Remove set slice from the fridge and cut into small squares.