In a small bowl, whisk together the cornstarch and cold water until completely smooth to create a slurry. Set aside.

In a separate bowl or measuring cup, crack the eggs and beat them thoroughly until well combined.

In a medium saucepan, combine the chicken broth, salt, white pepper, sugar, and turmeric (if using). Bring to a gentle boil over medium-high heat.

Stir the cornstarch slurry once more, then slowly pour it into the boiling broth while stirring continuously. Let simmer for 1-2 minutes until the broth thickens and becomes glossy.

Reduce the heat to medium-low so the soup is at a gentle simmer. Using a spoon or chopsticks, stir the broth in a slow, continuous circle to create a whirlpool.

Slowly drizzle the beaten eggs into the swirling broth in a thin, steady stream. The eggs will instantly cook into delicate ribbons. Stop stirring once the eggs are poured.

Remove the pot from the heat. Stir in the toasted sesame oil. Taste and adjust seasoning if necessary.

Ladle hot soup into bowls and garnish generously with chopped green onions. Serve immediately.