Grind the meat with the bacon, then add the chopped onion, egg, and slices of bread that have been soaked in a little water and then drained well. Season with the chopped parsley, salt and black pepper, then knead the mince well.
Heat oil on high heat and fry the shaped meatballs. Serve the meatballs with a sauce prepared by frying 2 tablespoons of flour in 2-3 tablespoons of butter. Be careful for it not to redden. Dilute gradually with some milk, add the tomato paste and let it boil for about 10 minutes. Remove from the heat, whisk 3 egg yolks and gradually add them to the sauce.