Step 1
Bring stock to a simmer in a medium saucepan over medium heat. Reduce heat to low and hold at a gentle simmer.
Step 2
Heat olive oil in a heavy-based saucepan over medium heat. Cook the onion and garlic, stirring, for 5 mins or until onion softens. Add the rice. Cook, stirring, for 2 mins or until grains appear glassy. Add the wine. Cook, stirring, until absorbed. Add 1/2 cup (125ml) of the stock and stir until completely absorbed. Continue adding 1/2 cupfuls of stock, stirring after each addition until liquid is absorbed, for 20 mins or until rice is tender. Stir in the tomato and parmesan. Set aside to cool.
Step 3
Line a baking tray with baking paper. Roll 1 tablespoonful of risotto mixture into a ball. Make an indent in the centre. Push 1 piece of bocconcini into indent. Use wet hands to enclose filling. Place on the tray. Repeat with the remaining risotto mixture and bocconcini.
Step 4
Place the flour, egg and breadcrumbs in separate bowls. Dip each risotto ball in flour to lightly coat. Dip in egg, then in breadcrumbs and shake off excess. Repeat with egg and breadcrumbs to double coat. Place on a lined tray. Place in the fridge for 30 mins to chill.
Step 5
Add enough vegetable oil to a medium saucepan to reach 6cm up the side of the pan. Heat to 180°C over high heat (when oil is ready a cube of bread turns golden brown in 15 secs). Carefully cook risotto balls, in 4 batches, for 3-4 mins or until golden and heated through. Use a slotted spoon to transfer to a plate lined with paper towel.
Step 6
Top with lemon zest to serve.
Tip: Make and crumb the risotto balls up to 2 days ahead. Store, in a single layer, in an airtight container in the fridge. Deep-fry just before serving.