Preheat oven to 200C. Grease a mini-muffin try and put aside.
1. Heat half the oil in a medium frying pan on low. Sauté onion until soft.
Add sugar and vinegar and stir until combined. Cook for 5 mins, until onion is caramelised.
Meanwhile, heat remaining oil in a large saucepan on high. Add rice and cook for 1 min or until rice is coated.
Add 2 1/4 cups of hot stock. Leave 1/4 cup aside. Stir and simmer on low for 15 mins, or until rice is soft. Remove from heat, add remaining stock, butter, 3/4 cup of parmesan and onions and stir until combined.
Transfer to a container and refrigerate overnight.
The following day, roll 1 tbsp of risotto mixture into balls and push a square of mozzarella into the middle. Then place into individual muffin trays and sprinkle with parmesan.
Bake for 20 minutes or until cooked through.
Serve at room temperature or cold.
