In a large bowl add all of the meatball mixture and mix to just combine. Do not overwork the meat as it will get tough. Using a small cookie scoop or a Tablespoon, scoop the meatballs into 1/2” round balls. Place on a parchment lined baking sheet or plate. Repeat to make all of the meatballs. Set aside.
In a large stock pot over medium heat add the oil. When the oil starts to shimmer add the onion, carrots and celery, stirring. Saute for 6-8 minutes or until the onions turn translucent. Add the stock and bring to a boil scraping the bottom. Once it starts to boil, add the meatballs, the Parmesan rind, pasta, and escarole. Continue to cook for 8-10 minutes or until the meatballs are cooked through stirring often. When the meatballs are fully cooked, remove the Parmesan rind and discard.
In a bowl whisk together the egg and 2 tablespoon of Parmesan cheese. Turn heat down on the soup to medium. Start stirring the soup around in a circle. Continue stirring and gradually drizzle in the egg mixture to form thin strands of egg; ~ 1 minute. Taste for seasoning and adjust accordingly.