In large saucepan, combine rice, broth, and butter or margarine. Bring to a boil, stir to blend. Reduce heat, cover, and simmer until liquid is absorbed, about 15 minutes. Set aside to cool. Stir in egg yolks and parmesan.
In small bowl, beat egg whites until frothy; set aside.
Cover and freeze rice mixture for 15 minutes to make them firmer to handle; roll them with your hands to form balls. Push a small cube of mozzarella into center of each arancini, lightly pressing to seal each ball. Roll each arancini in beaten egg whites, then coat with bread crumbs.
Preheat oven to 400 degrees (about 200 degrees Celsius). Heat oil in heavy skillet. Cook 8 rice balls at a time, about 4-5 minutes, turning frequently, to brown evenly. Place on baking sheet; bake for 10 minutes.
Serve with your favorite spaghetti sauce, to which you have added 3/4 cup to 1 cup of frozen green peas, uncooked.