To make the meatballs: Stir the first 6 ingredients in a large bowl to blend. Then add the Parmesan cheese, beef, and pork. Shape the meat mixture into meatballs, and place on a baking sheet. I prefer the meatballs to be on the smaller side, but you can make them any size you want.
To make the soup: Bring the broth and frozen 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 (approximately 20 minutes). Season with salt and pepper if needed. Sprinkle with parmesan cheese before serving, if you wish.
If you want more brothy soup, you can increase the broth, or use a little less pasta - about 6 oz.