Combine the meatball ingredients in a large bowl, using your hands, then form small balls from the mixture.
Heat some oil in a frying pan or deep-fryer, then fry them until golden all over. Drain the meatball on paper kitchen towels.
Make the tomato sauce: sauté the onion and garlic in oil. Add passata, stock and sugar. Season with salt, pepper and cayenne. Bring to the boil and simmer for 10 minutes under a lid or until you get a thick sauce. Mix in the meatballs, reheat, then serve with some chopped mint leaves.