In large, deep saucepan over medium-high heat, add the olive oil. Add the onions and saute for about 1 minute. Add the garlic stir. After another 5 minutes, add the rice and white wine and a pinch of salt stir and allow to cook down for about 5 to 10 minutes. Add 2 (8-ounce) ladles of broth. Allow to absorb into rice for about 10 minutes, stirring, then add another 2 (8-ounce ladles) of broth and allow that to absorb for about 10 minutes. Season with freshly ground black pepper, to taste. Add spinach to broth and rice and stir in with sweet butter. Add 1 cup of the Parmigiano. When all ingredients are hot and mixed, pour and spread onto a parchment lined cookie sheet to cool. Once cool, cover with a layer of plastic wrap to avoid skin forming and refrigerate until completely cooled and firm. Refrigerate overnight if necessary.
When completely cooled, cover rice and spinach with remaining 1/2 cup Parmigiano. With hands, roll into 1 1/2-inch balls. With fingers, make a small hole in the rice ball's center and insert 1 small cube of mozzarella, and cover with more rice.
Place flour, beaten eggs, and seasoned bread crumbs in separate bowls. Coat each ball with flour, then with whisked egg, then with seasoned breadcrumbs. Repeat with all rice balls and lay the coated balls on a cookie tray and refrigerate until ready to fry.
In a heavy large pan, heat vegetable oil to 350 degrees F.
Fry the balls, in batches, until golden brown. Remove each ball with a slotted spoon and place on parchment paper or paper towel lined cookie sheet to dry. Serve hot.