In a large bowl pour the meat, Parmesan cheese, softened bread, egg, parsley and garlic, nutmeg to your taste, salt and pepper. Start mixing with a fork and then with your hands to blend the ingredients well. Make this a quick operation so you don't heat the meat with your hands. The consistency should be soft and not too compact, if necessary add a few tablespoons of milk.
Create patties of the size you prefer, as equal to each other as possible, for even cooking. Store in the refrigerator.
In a large skillet put 4 tablespoons of oil and the vegetables (onion, carrot, celery) and cook over low heat. When they are almost golden brown, lightly flour the meatballs and, one by one, place them in the pan. You will need to brown them for about 1 minute and then turn them over and do the same.
Add the tomato, turn gently, cover and cook for about 10 minutes. Then start adding a small amount of salt, flip the meatballs and let them cook for another 10 minutes. Taste the sauce and decide if you want to add more salt and pepper, turn the meatballs again and finish cooking for another 5 to 10 minutes (depending on the size of the meatballs).
Leave to resto for 5 minute and serve.