Place all of the meatball ingredients in a large mixing bowl and, using your hands, combine until the ingredients are more or less evenly distributed. Break off about 1 tablespoon of the meat mixture and roll into a ball between your palms. Make sure they're small enough to sit comfortably on a soup spoon. Set aside. Continue with the remaining mixture. You'll have approximately 32 meatballs. You can make the meatballs ahead and refrigerate them, covered, at this point, if desired.

Heat a tablespoon of oil in a large, deep, wide-based, non-stick skillet or pot. Add the meatballs, leaving enough space between each so you can easily turn them. Depending on the size of your pan, you might need to do this in batches. Sear the meatballs on one side, then flip and sear on another side. Turn and sear the meatballs twice more so that they are mostly browned on the outside.

Add the chopped onions and mix with the meatballs, cooking until the onions are translucent. Pour in the marinara sauce and beef broth. Increase heat to medium-high and bring the soup to gentle boil, then reduce heat to medium-low to maintain a simmer.

While the soup is coming up to heat, bring a large pot of well-salted water to a boil, and cook the pasta according to the directions, minus 2 minutes of cooking time. (So, if instructions say to cook them for 7 minutes, cook for just 5.) Transfer drained noodles to the soup and turn heat to low. Let the soup rest for 5 minutes to finish cooking the noodles and to let them absorb the tomato broth.

To serve, ladle into bowls and top with additional parmesan cheese, if desired.