In a medium pot, bring the chicken or vegetable broth to a gentle boil. Stir in soy sauce and sesame oil. If you prefer a slightly thicker soup, whisk cornstarch with 2 tablespoons of water and stir it in.
Add the tofu cubes carefully into the broth and let them simmer for 2–3 minutes.
Reduce the heat to low. While gently stirring the broth in a circular motion, slowly drizzle in the beaten eggs. They will cook instantly, forming silky ribbons.
Season with white pepper and adjust salt as needed.
Garnish with sliced green onions and serve hot.