In a large pot, bring the chicken or vegetable broth to a gentle boil over medium-high heat.
Add the pastina to the boiling broth and cook according to the package instructions, usually about 5-7 minutes, until the pasta is tender. Stir occasionally to prevent sticking.
If you want to add eggs to the soup, beat the eggs in a small bowl. Once the pastina is cooked, reduce the heat to low and slowly drizzle the beaten eggs into the soup, stirring constantly to create egg ribbons.
Stir in the unsalted butter until it melts completely. Add the grated Parmesan cheese and stir until well combined and the cheese is melted into the broth.
Taste the soup and season with salt and pepper to your liking.
Ladle the soup into bowls and garnish with freshly chopped parsley if desired.
