Heat 1 tablespoon olive oil in a large saucepan over medium heat and add the onion, carrots, celery, and passata. Place the chicken drumsticks or legs in the saucepan, add the water, cover with a lid, and bring to a boil.
Remove the lid, add the half stock cube, if using, and season with Sea salt. Reduce the heat and simmer, uncovered, for 45 to 60 minutes, until the broth reduces slightly, concentrating its flavor.
Meanwhile, bring a saucepan of salted water to the boil and cook the pasta until al dente or according to package instructions. Drain and set aside. Strain the broth into a large, clean bowl and reserve the chicken and vegetables for another meal (such as adding them to some rewarmed leftover broth the next day when you’re feeling stronger and able to tolerate solid foods).
Divide the pasta among 4 shallow bowls and ladle the hot chicken broth over it. Sprinkle with the Parmesan and serve. [Editor’s Note: As one of our recipe testers said to us, “You may not think such a small amount of Parmesan would matter. It does.”]