For the rice: Bring 12 cups water to a boil and add rice. Reduce the heat and cook until the rice is sticky (a little overdone).
Mix the rice with Parmesan, pecorino and butter, then cool.
For the sauce: Saute red onion in olive oil in a saucepan until translucent. Add sirloin and cook until browned, then add San Marzano tomatoes. Mix in oregano, sugar, salt and pepper, then bring to a boil. Turn to low heat and simmer until the meat is tender, 45 minutes.
Add peas with 5 minutes left in the cooking time. Cool to room temperature.
For the arancini: Bring several inches oil to 350 degrees F in Dutch oven.
Scoop out some rice mixture and use a cupped hand as a mold to pat it together. Add meat sauce in the center. Cover the sauce with small strips of the mozzarella and close the ball. Dip the arancini in the eggs and coat with panko. Repeat with remaining ingredients.
Fry the arancini, turning once, until brown, 2 to 5 minutes. Serve with the meat sauce.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.