Pour the bone broth or chicken broth into a small saucepan.
Place the saucepan over medium-high heat.
Bring the broth to a rolling boil.
Season the boiling broth with fish sauce, Umami Stir-Fry Powder, or Diamond Crystal kosher salt to taste.
Taste the broth and adjust the seasoning as needed. The broth should be well seasoned before the egg is added.
Crack the egg into a small bowl.
Add a few drops of fish sauce and a small pinch of Umami Stir-Fry Powder or kosher salt to the egg.
Whisk the egg thoroughly with a fork until the yolk and white are fully combined.
Remove the saucepan from the heat once the broth is boiling and properly seasoned.
Using a heat-proof spatula, stir the hot broth in one direction.
While stirring, slowly pour the whisked egg into the hot broth in a thin stream.
Allow the egg to cook on contact with the hot broth. The egg should form soft, wispy ribbons.
Avoid over-stirring or returning the soup to high heat, as this may cause the egg to become firm or chunky.
Taste the soup once more and adjust the seasoning if necessary.
If using ground white pepper, add a small amount at this stage.
Transfer the soup to a serving bowl.
Garnish with thinly sliced scallion, cilantro leaves, and sliced hot chili peppers, if desired.
For a heartier serving, top the soup with crisped Kalua Pork or another cooked protein.
Serve immediately while hot.