Prepare the risotto mixture: In a large bowl, combine the cooled risotto, grated Parmesan cheese, and 1 egg. Mix well until fully combined.

Shape the arancini: Take a small handful of the risotto mixture and flatten it in your palm. Place a cube of mozzarella in the center, then shape the risotto around it to form a ball.

Coat the arancini: Set up a breading station with three bowls—one with flour, one with beaten eggs, and one with breadcrumbs. Roll each ball in flour, dip in egg, then coat with breadcrumbs.

Heat the oil: In a deep pan, heat vegetable oil to 350°F (175°C). Ensure there’s enough oil to submerge the arancini halfway.

Fry the arancini: Carefully place the coated arancini into the hot oil. Fry in batches for 3-4 minutes, turning occasionally, until golden brown and crispy.

Drain and serve: Remove the arancini with a slotted spoon and place them on a paper towel-lined plate to drain excess oil. Serve hot with marinara sauce for dipping.