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