Grease two 18X28cm rectangular slice tins and set aside.
Place the parmesan cheese and cheddar cheese into the Thermomix bowl.
Grate on Speed 9, 10 seconds. Set aside in a seperate bowl.
Wash and dry the Thermomix bowl.
Add the rosemary leaves and garlic to the Thermomix bowl.
Finally grate on Speed 7, 10 seconds. Scrape and repeat until finely chopped.
Add the water and heat for 8 minutes, Varoma, Speed 2.
Set the Thermomix to Varoma, 3 minutes, Speed 2 and slowly add the polenta through the MC hole (while the blades are turning).
Place the MC lid back on (to prevent any mixture bubbling out).
Add the butter, cheese and sea salt and slowly increase to Speed 7, 1 minute (if the Thermomix starts shaking, turn the Speed down and continue to increase slowly).
Quickly pour the mixture between the two prepared tins and place onto the bench to set for 20 minutes.
Place into the fridge until completely cold.
Cut into 'chip' sized pieces.
At this stage you can either bake the polenta chips on a baking tray in the oven (200 degrees celsius fan-forced) for 20-30 minutes or until crispy on the outside, or you can freeze them in an airtight container (with a sheet of baking paper between each layer).
The polenta chips can then be cooked as per usual from frozen.