Finely chop the onion. Heat the chicken stock in a pot and add the dried mushrooms. Set aside.
In a large pot, heat the butter and brown the onion for 5 minutes. Add the arborio rice and mix well to coat. Cook a minute longer then deglaze with the white wine. Mix well and let liquid evaporate.
Add one ladle of chicken stock at a time stirring frequently until the liquid is completely evaporated after each addition. Repeat the operation until the rice is al dente or for about 20 minutes. Slice the Cacciatora sausage and cut the slices in small pieces.
Off the heat add the parmesan and sausage pieces and pepper generously.
Let the risotto cool at least 1 hour.
Prepare 3 deep plates for breading: 1 with the flour, one with the 3 beaten eggs, and the last with the panko.
Once the risotto has cooled, using your hands form ping pong ball sized rice balls.
Coat balls in flour, shaking off any excess. Dip into the egg wash then roll through the breading.
In a large pot, heat an adequate amount of oil, fry 8 balls at a time until well browned. Drain on paper towels.
You can freeze cooked arancini and reheat them on a baking sheet for about 15 minutes in an oven preheated to 350°F.