In a medium mixing bowl, add the chilled risotto, the mozzarella cheese, and the Parmesan cheese and mix together well.
Dip fingers in water and shape 2 rounded tablespoons chilled risotto mixture into a (1 1/2-inch) ball. Roll in palm of hands to make a smooth ball. Place ball on a baking sheet lined with waxed paper. Repeat until you have formed 32 balls. Cover with plastic wrap and store in refrigeration until ready to fry. (The recipe may be prepared a day in advance to this point.)
In a large pot or Dutch Oven, heat oil to 360-370 degrees F. (Use a deep fat or candy thermometer to gauge the temperature).
Put flour, eggs and bread crumbs in separate bowls. For each risotto ball: roll in flour and shake off excess; dip in egg and let excess drip off; roll in bread crumbs; transfer to a baking sheet lined with waxed paper.
Using a metal slotted spoon or skimmer, lower six balls into the oil. Fry until golden brown, approximately 3 to 3 1/2 minutes per batch of six. Transfer to a paper towel to drain. Repeat until all the balls are fried.
The risotto balls are best if served immediately. They may be held in a 250 degrees F oven while the remaining balls are fried.