Directions

1. For the Meatballs: Preheat oven to 400°F. Line a half sheet pan with parchment paper or non-stick-sprayed foil. To a large bowl add torn bread and grated onion. Mix to combine and let sit for 1 minute. Add the Parmesan cheese, egg, garlic, Italian seasoning, and salt and pepper to taste. Stir to combine. Crumble ground pork over the top then use your hands to mix until just combined.
2. Use a teaspoon to portion meatballs out, then gently roll in your hands and place on a prepared baking sheet. The meatballs can be very close together, but not touching. Bake for 25-30 minutes, or until golden brown and cooked to an internal temperature of 160°F. Set meatballs aside. Meatballs can be cooked and then cooled and refrigerated a few days ahead of time.
3. Meanwhile, heat extra-virgin olive oil in a large soup pot or Dutch oven over medium heat. Add carrots, celery, and chopped shallot or onion. Season with salt and pepper, then sauté until the vegetables are tender, 8-10 minutes.
4. Add chicken stock and Parmesan cheese rind (if using), then turn heat up to high to bring liquid to a boil. Add the pasta and turn heat down to medium-low. Simmer until pasta is al dente, about 20 minutes. Add cooked meatballs and stir to combine. Bring soup back up to a low boil, increasing the heat if needed. Add spinach and cook until wilted and tender, 2-3 minutes.
5. Whisk the egg and Parmesan cheese together very well in a small dish. Give the soup a couple of big stirs to get the liquid swirling in one direction, then slowly stream in egg mixture. Continue to stir to create small threads of egg. Taste and add more salt and/or pepper if desired. Let soup sit and thicken for 10-15 minutes before removing the Parmesan cheese rind. Ladle into bowls, and serve.