Warm the oil in a large non-stick pan over a medium heat.
Add the onion and garlic and a pinch of salt and pepper. Fry for 3-5 minutes until softening.
Add the rice and stir for a minute or so until glossy
Add quarter of the stock and cook gently while stirring.
When the liquid has absorbed, add another ladleful of stock. Keep stirring and adding until the rice tastes cooked and the liquid has been absorbed.This whole process should take about 20 minutes in total.
Stir in the hard cheese, season to taste, then transfer to a tray and spread out to encourage it to cool as rapidly as possible.
Once cool, cover and place in the fridge to chill - cold risotto is much easier to shape.
Make the arancini
Preheat the oven to 200C (180C fan).
Divide the risotto mix into 20 equal portions. If you would like your arancini to be very evenly sized, you can either use an ice cream scoop, or you can weigh the risotto and then divide by 20 to work out the exact weight of each ball. This will vary slightly according to the exact amount of liquid added and absorbed - in my case, each ball weighed 45g.
Take a ball and flatten in your hand.
Place a piece of mozzarella in the centre, then squeeze the risotto around it. Roll in your hands to form a ball. Do your best to keep the cheese in the centre as it may cause the arancini to burst if it is near one side.
Repeat until all the risotto is used up.
Bread the arancini
Prepare three bowls, one containing the flour, one containing the beaten egg and one containing the breadcrumbs and paprika. Season all three bowls then stir in the seasonings and beat the egg.
One by one, dip the arancini first in the flour, then in hte egg, then in the breadcrumbs. Be sure to coat all over with each step.
Place your arancini on a non-stick baking sheet lined with baking paper as you go, repeat until you've breaded all twenty.