Bring 4 1/2 cups chicken broth to a boil in a medium saucepan. Stir in the pastina and reduce the heat as needed to maintain a steady simmer. Cook, stirring frequently, according to the package directions for firm or al dente pasta, about 5 to 7 minutes. Add extra broth as needed if the mixture thickens before the pastina is tender.
Tip: Pastina tends to stick, so stir frequently, especially at the beginning and again near the end as it thickens.
Meanwhile, combine the Parmesan cheese, egg, and freshly ground black pepper in a bowl, and whisk to blend.
1/2 cup grated Parmesan cheese | 1 large egg | 1/4 tsp freshly ground black pepper
Add a ladleful of the hot pastina mixture to the egg mixture while whisking briskly to temper the egg. Stir the egg mixture back into the pot and continue stirring for 1 to 2 minutes, or until the mixture is creamy, the cheese is melted, and the egg is cooked by the residual heat. Do not boil. Taste and season with kosher salt, if needed.
Kosher salt
Tip: If the pastina has cooled slightly before you stir in the egg mixture, place the pan over the lowest heat and cook, stirring constantly, for 1 to 2 minutes. The mixture should register 160°F or higher after the egg is added. Do not let it boil.
Serve the pastina hot with extra Parmesan cheese and a garnish of chopped parsley or chives, if desired.