For the meatballs:
Place the first six ingredients (onion, parsley, egg, garlic, salt, and bread) in a large bowl to blend. Then add the cheese, beef, and pork. Shape the mixture into small meatballs and place on a sheet pan. Typically, the meatballs for this soup are fairly small, but you can make them any size you want.
To make the soup:
Bring the stock and spinach to a boil in a large pot. Add the meatballs (uncooked) and simmer for a few minutes, stirring occasionally to make sure they don’t stick. Add the pasta and continue cooking at a low boil until both the pasta and meatballs are cooked, ~15 minutes. Taste and then season with salt and pepper as needed. Sprinkle with Parmesan cheese before serving