Make the tomato sauce

1. In a pot, heat 1 tablespoon olive oil. Add the ground beef, garlic, carrot, onion and celery pieces and cook until beef is browned. Keep breaking up the beef as it cooks to form small bits. Once the meat is browned, add the tomatoes. Let the sauce come to a boil then reduce heat to medium-low heat, cover and let simmer for about 45 minutes. Stir frequently to prevent it from sticking to the bottom of the pot. Once cooked, remove the garlic, carrot, onion and celery pieces.
2. Cook the rice in plenty of salted water for 12 minutes (until al dente) then drain and spread out onto a tray. While the rice is still warm, add the sauce, parmesan cheese and butter and mix well until uniform.
3. Let this mixture cool completely.
4. Then add the eggs and again mix well.
5. To form the arancini, take about 1/3 cup of rice mixture and with your hands, shape it into a small ball.
6. Make a well in the centre of the rice ball and insert a couple mozzarella cubes.
7. Work the rice so that it completely encloses the cheese and re-shape into a smooth ball. You want to make sure that the arancini at this point are firm so they do not fall apart while cooking.
8. Once all of the rice balls are formed, roll them one at a time in the bread crumbs and press lightly to coat.
9. Place them on a clean baking sheet
10. Put enough oil into a heavy-bottom pan to fully submerge the rice balls
11. Place the oil over high heat. Check that the oil is ready by carefully dipping one rice ball in. It should be a lively but steady sizzle.
12. When the oil is to temperature, carefully add in a batch of the rice balls (do not overcrowd).
13. Let the rice balls fry in the oil, turning as necessary, until golden brown on all sides (about 5 minutes).
14. With a slotted spoon, remove the cooked rice balls from the oil and place on a paper towel lined baking sheet.