Remove the rind from the Fontina and cut it into cubes. Heat the broth, finely chop the onion and stew it in a thick-bottomed pot with half of the butter. After a couple of minutes add the rice, toast it, add salt and wine, add a ladleful of hot broth and cook it, stirring often and adding a little broth at a time.
When the rice is cooked and dry (it should not be watery) remove it from the heat, add the remaining butter and the Fontina, except for a handful of cubes. Add salt and pepper to taste, mix well, place on a baking tray, cover with cling film and allow to cool to room temperature.
Transfer the cooled rice into a bowl, add the egg yolks, finely chopped chives and a couple of tablespoons of breadcrumbs to make a fairly firm mixture. Mix well and, with wet hands, form into croquettes of about 40 g each, inserting a cube of Fontina in the middle.
Dip the croquettes in breadcrumbs, line a baking tray with kitchen paper, heat 2 fingers of oil in a large frying pan without making it smoke and fry the croquettes on both sides until lightly golden. Drain the croquettes on the kitchen paper to drain off the excess oil and serve hot with a chive-scented tomato sauce.
