Add the egg, the 1/2 cup breadcrumbs and the parsley to the cooled risotto. Shape the mixture into twelve 1 1/2-inch balls.
Press your finger into the center of each ball and insert the Fontina cheese cube. Then, pinch the risotto mixture around the filling to enclose, adding a little more if necessary.
Add the remaining breadcrumbs to a shallow bowl. Roll each risotto ball in the breadcrumbs and place on a parchment paper lined baking sheet. Loosely cover and refrigerate for 1 hour.
In a heavy bottomed pot, heat enough vegetable oil to cover the balls, over medium heat until a deep fry thermometer registers 350 degrees F.
Fry the arancini, working in batches, until golden brown on all sides, about 4 minutes. Be careful so the oil doesn't get too hot or the balls will burn on the outside and the cheese won't melt!
Remove the balls with a slotted spoon and drain on paper towels.
If desired, heat the marinara sauce so it's warm for serving.
Serve the hot arancini balls with the marinara sauce dip!