Finely grate 1 ounce Parmesan cheese (about 1/2 firmly packed cup), or measure out 1/3 cup store-bought grated.

Measure 3 cups of the broth into a large saucepan. Add 1 (12-ounce) box pastina and bring to a gentle boil over medium-high heat, stirring occasionally. Continue to cooking, stirring often, until the pasta is al dente and there is a small amount of liquid left in the pan, about 6 minutes. (Add the remaining 1 cup broth a little at a time as needed if you need more liquid.)

Turn off the heat. Immediately add the Parmesan, 1 large egg, and 1/4 teaspoon black pepper. Quickly stir to incorporate the egg into the warm pasta and melt the cheese. Serve topped with more grated Parmesan or freshly ground black pepper.