Soak the bread in the milk in a bowl for a few minutes. When all the milk is absorbed, mash the soggy bread into a paste.
In a frying pan, sauté the onions with the olive oil over a gentle heat until softened. Leave to cool down.
Squeeze out any excess moisture from the bread and place it into a large bowl together with the minced beef and pork, the softened onions, the egg, Par