Clean the fillet, cut it finely with a knife and season with salt, pepper and oil.
 Peel the onions, slice them thinly and cook them with vinegar, salt and sugar for about 20 minutes until soft and caramelized.
 Finely chop the rosemary,
 Toast the rice with a drizzle of oil, cook with the broth and bring to the boil. 
Stir in butter and parmesan, place the risotto on a flat plate, top with the chopped meatballs and the caramelized onions in the center.
 Photo: Stefano Borghesi Photographer