Heat half of the oil in a saucepan, add the onion and garlic and cook for a few minutes, until soft but not browned.
Add the rice and stir well. Slowly add the broth and stir until the rice has absorbed the liquid. Continue adding broth until the rice is slightly softened and not mushy. Add butter, parmesan and stir well. Transfer to a bowl and refrigerate.
Blend the basil leaves with the remaining olive oil until a thick mixture is formed. Pour the oil and basil mixture into the rice, stir well and place back in the refrigerator to cool completely.
Once the rice has cooled, mold into 20 balls. Press 1 feta cheese cube into the centre of each ball, sealing it inside. Dust the rice balls with flour, dip them in the egg and then coat with bread crumbs.
Heat the sunflower oil in a deep frying pan and fry the balls for 2-3 minutes, until browned. Place the rice balls on a plate lined with paper towel to absorb any excess oil.
Transfer the rice balls to a serving dish, garnish with basil leaves and serve.