Soak the bread in the milk until the liquid is absorbed, about 8 minutes. Meanwhile, combine the ground beef and pork in a bowl with the egg, cheese, minced garlic, parsley, 1 teaspoon salt, and pepper to taste. Add the soaked bread and mix with your hands until combined. Form into 16 meatballs.
Heat the olive oil in a heavy-bottomed pot over medium heat. Add the meatballs and cook, turning, until browned on all sides, about 10 minutes. Transfer to a paper-towel-lined plate. Add the beef shin and sausage to the pot and cook until browned, turning, about 10 minutes. Transfer the meats to a large bowl.
Add the onion and smashed garlic to the pot and fry until soft, about 4 minutes.
Crush the tomatoes into the pot with your hands and pour in the juices. Stir in the tomato paste, season with salt and pepper and cook 5 minutes.
Add 5 cups water and the bay leaves, then return the meatballs, beef shin and sausage to the pot, stirring carefully. Bring to a low boil, stir, then reduce the heat to low. Cover and simmer 2 hours, or until the shin meat is very tender. Uncover and simmer until the sauce thickens and the shin meat is falling off the bone, about 1 hour 30 minutes. Transfer all the meats with a slotted spoon to a bowl and cover with foil. Simmer the sauce to thicken, about 20 minutes. Discard the bay leaves.
Meanwhile, bring a large pot of salted water to a boil; add the pasta and cook as the label directs. Drain and toss with enough sauce to coat lightly, then top with more sauce and the meat. Garnish with parmesan, if desired.