Bring the broth to a boil in a large saucepan over medium-high heat. In a bowl, whisk the eggs, cheese, parsley, and basil to blend. Reduce the heat to medium-low. Stir the broth in a circular motion. Gradually drizzle the egg mixture into the moving broth, stirring gently with a fork to form thin strands of egg, about 1 minute. Stir in the spinach, then season the soup, to taste, with salt and pepper.
Ladle the soup into bowls and serve.