In a medium saucepan, bring the broth to a boil and add the saffron and the cheese rinds. Turn the heat to very low and keep warm while the saffron releases its beautiful flavor.
Melt 2 tablespoons of the butter in a large saucepan over high heat. Add the Arborio rice and immediately reduce the heat to medium-high. Cook the rice for a few minutes, or until the grains are becoming translucent. Add the warm broth, 2 ladlefuls at a time, cooking and stirring continuously until all the liquid has been added. Allow each addition of broth to be absorbed almost completely before adding more. This process will take about 20 minutes. Once the rice is just al dente (don’t overcook the rice or it will become mushy), turn the heat off and add the remaining 2 tablespoons of the butter, the Parmesan, and egg yolk. Pour the risotto out onto a baking sheet and let cool until you can handle it with your hands. Roll the rice into balls roughly the size of golf balls.
Set up your breading station in 3 separate shallow dishes, with the flour in the first dish, the lightly beaten egg whites in the second, and the bread crumbs in the third. Roll the risotto balls in the flour, then the egg, and lastly in the bread crumbs, setting them on a baking sheet as you go. In a deep, heavy pot, heat about 6 inches of vegetable oil to 350°F. For safety reasons, never fill the pot more than halfway with oil. Working in batches, gently lower the balls into the oil and cook until golden brown, 4 to 5 minutes. Don’t cook more than 8 or 10 at a time; this ensures that the oil will stay nice and hot. Use a slotted spoon to transfer the fried arancini to paper towels to drain and keep warm while you fry the remaining rice balls. Serve hot.