Freeze the chilli in an ice cube tray. Depending on the size of your cubes you should have enough rice to make roughly 6 arancini (use the rest another time).
In a microwaveable bowl pour the rice and stock. Cover with clingfilm. Stir and then microwave on full for 6 minutes, then remove clingfilm and microwave for a further 10.
Stir in the butter, parmesan and cheddar then spread in a baking tray - this helps it cool and ensures you have an even amount of rice on your arancini.
Take the iced chilli cubes from the freezer and a handful of the sticky rice mixture - shape this around the chilli in your palm and roll to make a ball.
Get your oil up to 170°C/340°F.
Roll the rice balls in flour, then dip in egg and finally roll in breadcrumbs, then dip in the egg again and finally back in the breadcrumbs. Fry in batches of 2 until golden and crisp (roughly 4 minutes).