Roll chilled risotto into 12 (1 1/2-inch) balls using wet hands. Poke a small hole in center of each ball and insert a cube of cheese, then re-form into a ball.
Put flour, eggs, and bread crumbs in 3 separate bowls. Dredge 1 risotto ball in flour, shaking off excess. Dip in egg, letting excess drip off, then dredge in bread crumbs and transfer to a sheet of wax paper. Repeat with remaining balls.
Heat 1 1/2 to 2 inches oil in a 4- to 5-quart heavy pot until thermometer registers 360°F. Working in batches of 4, lower rice balls into oil with a slotted spoon and fry, turning occasionally, until golden brown, 2 to 3 minutes per batch. Transfer with slotted spoon to paper towels to drain. Return oil to 360°F between batches. 3Let balls stand 2 minutes (for cheese to melt).
