Combine the risotto, beaten egg, and prosciutto a large bowl and mix 'em well. Press 2 tablespoons of the risotto mixture around 1 cube of provolone to form a small ball. Do this until you've used up all of the risotto and cheese.

Place the flour in a shallow bowl, then place the breadcrumbs in a second shallow bowl. Beat the egg with 2 tablespoons of water in a third bowl. Dredge the rice balls in the flour, dip them in the egg mixture, and roll them in the crumbs to get a nice, even coat. Place each ball on a tray, cover it loosely with plastic wrap, and let them chill for at least 30 minutes (though they're okay to leave for up to a day).

Pour oil to a depth of 3 inches in a deep saucepan and turn the heat up to 350°. Fry the rice balls in batches for 4 to 5 minutes or until golden. Remove the balls from the oil with a slotted spoon and let them drain on paper towels. Serve warm.