Make the Rice • In a large saucepan over medium-high heat, place the rice, saffron and 1 1/2 cups water. Bring to a boil, cover, and reduce heat to low. Let simmer about 15 to 20 minutes or until all of the water has been absorbed. • Remove lid, stir in grated Parmigiano, butter, salt and pepper to taste. Spread the rice out on a large plate or baking dish to cool completely to room temperature. Meat filling • First, you'll start with a classic soffritto: Heat the olive oil in a small saucepan over medium-high heat. Add the onions, carrots, and celery and sauté, stirring often, until softened and the onions are translucent, about 8 to 10 minutes. • Add the ground beef and pork and fry, stirring often, until browned, about 5 to 8 minutes. Add the wine and let cook until the alcohol aroma has reduced, about 1 minute. • Stir in the tomato paste and tomato purée, reduce the heat to medium-low, and cook, stirring occasionally, about 10 minutes. • Add the peas and continue to simmer the sauce for another 8 to 10 minutes, or until the peas are tender and the sauce is thickened. It should not be too liquidy. • Transfer the filling to a bowl and set aside to let it cool. Assemble and Fry the Arancini • Once the rice and filling are completely cooled, start shaping your rice balls. • Place 1 heaping tablespoon of rice in the palm of one hand, then use your fingers and thumb to shape it into a hollow bowl shape. • Place about 1 teaspoon of the filling in the center, 1 to 2 small cubes of diced fresh mozzarella (if using), and then gently close the rice around the filling to form either a round ball shape or a cone/pear shape. • When all of your arancini have been formed, whisk together the flour, eggs, 1/2 cup of water and a pinch of salt in a shallow bowl until smooth. Spread the bread crumbs in a plate or baking dish. • Gently roll each ball first in the egg-flour-water-salt mixture, letting any excess drip off, then in the breadcrumbs until evenly coated. • At this point, you can refrigerate your arancini for 20 to 30 minutes to let them firm up, if they seem a bit too loose or liquidy. If not, you can go directly to frying. • Heat about 2 inches (5 cm) of neutral frying oil to 360 F (182 C). Fry your arancini in batches of just 2 to 3 at a time, being careful not to overcrowd the pot, until they are evenly golden-brown, about 3 minutes. • Transfer them to a paper-towel lined plate to drain and serve hot.