For the meatballs:
1/3 cup Italian-style breadcrumbs
1/4 cup finely grated Parmesan or Pecorino Romano cheese
1 large egg, lightly beaten
1 small garlic clove, minced
1/2 teaspoon black pepper
1/2 teaspoon kosher salt
1 pound ground beef
For the soup:
2 tablespoons olive oil
2 to 3 large celery stalks, finely chopped
2 medium carrots, peeled and sliced into rounds
1/4 teaspoon kosher salt, plus more to taste
1 small yellow onion, minced
6 cups chicken broth, plus 1 to 2 additional cups if desired
1 28-ounce can diced tomatoes
1 head escarole or 1 bunch spinach, rinsed and torn into bite-sized pieces
8 ounces (1/2 pound) small pasta, such as acini di pepe
2 large eggs
1/4 cup finely grated Parmesan or Pecorino Romano cheese
1/2 teaspoon black pepper
Kosher salt as needed
Make the meatballs: Whisk the breadcrumbs, cheese, egg, minced garlic, pepper, and salt together in a large bowl. Add the beef and mix with your hands until incorporated. The blend will be closer to a meatloaf situation than a typical meatball; I like them to be a little sturdier as they simmer in the sauce.
Roll into small balls about 1 inch in diameter — you'll have about 6 dozen when you're done. Place the meatballs on a rimmed baking sheet as you roll and set aside while you start making the soup.
Make the soup: Heat the oil in a large (6- to 8- quart) stockpot or Dutch oven over medium heat. Stir in the celery, carrots, and onion, along with 1/4 teaspoon salt, and cook until the vegetables are just starting to turn translucent and tender.
Pour in 6 cups broth and the can of diced tomatoes, and bring to a boil. Add the meatballs and cover to return the liquid to a boil. Cook for about 5 minutes.
Uncover the pot and stir in the escarole a few handfuls at a time, letting each handful start to wilt and make more room in the pot before adding the next. Return the soup to a simmer and cook for 10 minutes more, until the greens are tender.
If you're planning to freeze the soup, stop cooking the soup after the greens are tender. See below for freezing and thawing instructions.
With the soup simmering, add the pasta and cook for 10 minutes until al dente. Add 1 to 2 cups additional broth if you prefer a more brothy soup.
While the soup simmers, whisk the eggs with the cheese and black pepper. When the pasta is still slightly underdone, pour the whisked egg into the simmering soup, drizzling evenly across the top of the soup to create a thin layer of egg. Let cook without s