In a small saucepan, bring beef bone broth to a boil.
In the meanwhile, beat the eggs in a small bowl, dissolve cornstarch in cold water in another small bowl, and chop the green onion. Set aside.
Once the broth is boiling, stir in dissolved cornstarch, followed by the beaten eggs. Then immediately start stirring so that the eggs are evenly distributed in the broth; stir constantly for 30 seconds, or until the soup is thickened.
Turn off the heat; taste and add a pinch a salt if desired. Dish, drizzle with sesame oil and garnish with green onion. Serve immediately.