Reconstitute the mushrooms in lukewarm water, chop and set aside. Sauté one onion in 2 oz. butter in a saucepan. When the onions are soft, add the rice. Make a risotto as in basic recipe and let it cool.
Make a ragù by sautéing one onion in the remaining butter. When onions are soft, add the chopped livers, veal, prosciutto, and mushrooms. Add the tomato paste diluted in 1 cup warm water, salt and let simmer over a low flame. Let the mixture cook and reduce to achieve a rather thick ragù. Remove from heat and cool.
Take a small amount of rice in the palm of your hand, flatten the rice and place in the center a teaspoonful of the prepared ragù, and few pieces of Mozzarella. Close your palm and form a ball. Make sure the filling is securely closed in the center of the ball (twice the size of a walnut). Roll the rice ball into flour, beaten egg and breadcrumbs, continue until the rice is finished.
Fry the supplì in hot oil until golden brown and crunchy. Serve immediately, plain or with a tomato or meat sauce on the side.
