01 - Bring the chicken or vegetable broth to a gentle simmer in a medium saucepan over medium heat.
02 - In a mixing bowl, whisk together the eggs, grated Parmesan, breadcrumbs (if using), parsley, salt, and pepper until well combined.
03 - Reduce heat to low. Slowly drizzle the egg mixture into the simmering broth while stirring continuously with a fork or whisk. The eggs will form delicate, wispy ribbons throughout the broth.
04 - Stir in the chopped spinach (if using) and cook gently until just wilted, about 1 minute. Taste and adjust seasoning with salt and pepper as needed.
05 - Ladle into bowls and serve hot, garnished with additional grated Parmesan cheese if desired.