Bring the stock to a boil in a wide, shallow pan or saucepan. Add the pastina, then reduce the heat to a simmer. Cook for 7–8 minutes, stirring regularly, until tender and at your desired consistency. There should still be some stock remaining around the pasta.
Remove from the heat and stir through the butter until melted.
Add the parmesan in two separate additions, stirring well and allowing the first addition to melt completely before adding the second.
Finish with a squeeze of fresh lemon juice, if desired (highly recommended!), and serve immediately.
Adjust the consistency if needed. The recipe as written gives you my preferred middle ground consistency. Add a little more stock for a brothy, soup like pastina or keep it as is for a thicker finish.
Notes
Stock amount - Adjust to your preferred consistency. Use more stock for a brothy, soup like pastina or less for a thicker, risotto style finish. My recipe lands somewhere in the middle.Seasoning - I don't add any salt as the stock and parmesan provide plenty. Taste at the end and season if needed. Add ¼-½ teaspoon of black pepper if desired.Parmesan - Finely grate it yourself so it melts smoothly. I use a weight measurement here as the amount in a cup can vary hugely depending on how finely the cheese is grated and how tightly it’s packed.Lemon - Optional, but highly recommended! A generous squeeze at the end cuts through the richness of the butter and parmesan.