Taste and adjust the seasoning: the broth should taste like a well-seasoned chicken soup.
Cornstarch Slurry
In a small bowl, mix the cornstarch and cold water.
2 tablespoons cornstarch, 2 tablespoons water
Stir until you have a smooth liquid: the mixture resists at first, so keep stirring for a few seconds.
Bring the broth back to a simmer.
Stir the cornstarch mixture once more, as it settles quickly.
Slowly pour it into the broth in a thin stream, stirring constantly.
Simmer for 1 to 3 minutes, until the broth has some body and lightly coats a spoon, without being as thick as a sauce.
Eggs
Beat the eggs with the water until the mixture is completely smooth, with no visible white.
2 eggs, 1-2 teaspoons water
Beat with a fork or chopsticks, without beating in any air.
Lower the heat so the broth is just below a simmer, not boiling.
Gently stir the broth in one direction only.
Pour in the eggs in a very thin stream, still stirring gently in the same direction.
Once all the eggs are in, simmer gently for 1 to 2 minutes so they cook through.
Taste and adjust the seasoning one last time.
Sprinkle with the sliced green onion and serve.
1-2 green onions,
Notes
For the yellow color you see in restaurants, add 0.5 teaspoon of ground turmeric along with the other seasonings, or a few drops of yellow food coloring. This is purely cosmetic.If the broth is too thick, add a little water, then adjust the seasoning. If it is too thin, mix 1 tablespoon of cornstarch with 1 tablespoon of cold water and pour it in in a thin stream. Tapioca starch can be used in place of cornstarch.A very thin stream gives fine, light strands, restaurant style. A thicker, faster stream gives larger pieces. If the broth is boiling when you add the eggs, they cook too fast, toughen and cloud the soup.You can add corn, carrot, peas or mushrooms: cook them in the broth before adding the cornstarch slurry and the eggs.The broth without the eggs keeps for 3 to 4 days in the fridge and can be frozen. When ready to serve, bring it to a simmer and pour in fresh eggs: reheated eggs turn rubbery.