Add the stock to a medium saucepan and bring it to a boil.
Stir in the pastina and reduce the heat to low. Simmer for about 5-6 minutes, stirring frequently, until most of the stock is absorbed.
Whisk the egg in a small bowl until completely combined.
When there is just a bit of stock remaining in the saucepan, turn off the heat.
Mix in the remaining ingredients one at a time: butter, Parmesan cheese, and beaten egg.
Add salt to taste.
Ladle the pastina into bowls and top with black pepper, extra Parmesan cheese, and olive oil.
