Line 2 baking trays with greaseproof paper and set aside.
Heat the olive oil in a heavy-based saucepan.
Add the onion, cover and fry until soft. In another pan, mix in the passata and stock, and warm over a low heat.
Add the garlic to the onion, cook for 30 seconds, then tip in the rice and stir to coat in the oil.
Increase the heat, pour in the wine and let it simmer until absorbed.
Keeping the pan over a medium heat, start adding the tomato stock mixture to the rice a ladleful at a time, each time allowing the rice to absorb the liquid.
Keep stirring, adding liquid until the rice still has a light bite.
Turn off the heat, stir through the parmesan, butter and basil, then cover for 5 minutes.
Season with salt and pepper and tip onto the tray to cool completely, then chill until firm.
Shape the risotto into 12 large balls.
Make a hole in the centre with your finger and stuff in a piece of mozzarella, then reshape into a ball.
Dip the balls in the flour, then the egg then finally the breadcrumbs and chill for 30 minutes.
Heat the oil to 160C or until a torn piece of bread tossed in gently turns golden brown in 10 seconds in a large deep saucepan and preheat the oven to 180°C / 350°F / Gas mark 4.
Lower the risotto balls into the oil and deep-fry them for 8-10 minutes in batches.
Drain on kitchen paper, then transfer to a tray and bake in the oven for 6-8 minutes.
Sprinkle with salt, then leave to cool for a few moments before serving with a salad.