In a measuring cup with a spout or a small bowl, beat the eggs until smooth and set aside. (Tip: Using a measuring cup with a spout helps to create even, thin egg ribbons later).
In a separate small bowl, combine the cornstarch and water until starch has dissolved and set aside. This is your cornstarch slurry.
In a medium pot, add chicken stock and scallion whites only. Cover and bring to boil over medium-high heat.
Reduce to medium heat and mix the cornstarch slurry first. Then while stirring, pour the cornstarch slurry into the broth. Let it come to a boil on medium heat until thickened, about 1-2 minutes.
Season broth with chicken stock powder, sesame oil, salt and white pepper and stir.
While stirring, pour the eggs in a thin stream from a slight height to create smaller egg ribbons. (For larger egg ribbons: without stirring, pour eggs at a lower height and let it set for 10 seconds and then gently stir).
Simmer the soup for 1 minute. Remove off heat and garnish with scallion greens. Enjoy!