Stir together the risotto and egg until thoroughly combined. Put the breadcrumbs in a shallow bowl. Roll a small handful of risotto into a ball about 1-1/2 inches in diameter, gently push a cube of mozzarella into the center, and reshape the ball, covering the cheese completely. Coat in the breadcrumbs and transfer to a plate. Repeat until all of the risotto is used.
Pour the vegetable oil into a 3-quart saucepan and heat to 350°F over medium-high heat. Working in batches of 5 or 6, fry the arancini, turning occasionally, until browned and heated through, about 4 minutes. Transfer to a plate lined with paper towels to drain. Sprinkle with salt and serve.
nutrition information (per serving):
Photo: Scott Phillips