Prepare the Risotto: Rinse 1 cup of Arborio rice under cold water until the water runs clear. In a pot, combine the rice with 3 cups of broth and simmer on low heat for about 20 minutes. Season with salt and pepper, and let it cool for at least an hour in the refrigerator.

Form the Balls: Scoop out a portion of risotto, flatten it slightly, place a square of mozzarella cheese in the center, fold the rice around the cheese and shape it into a tight ball.

Coat the Balls: Whisk 2 eggs in one shallow dish and place panko breadcrumbs in another. Roll each risotto ball first in the beaten eggs, then coat it thoroughly in breadcrumbs.

Fry the Arancini: Heat vegetable oil to 350°F (175°C). Carefully add a batch of arancini to the hot oil, fry for about 4-5 minutes until golden brown.

Drain and Serve: Place the arancini on paper towels, then transfer them to a serving platter. Serve hot with marinara sauce.