How to Make It
Bring the stock, ginger, and 1 teaspoon salt and 1/2 teaspoon pepper to a boil in a medium saucepan.
Stir together the soy and corn starch, then whisk into the broth and boil until the soup is slightly thickened, 1 to 2 minutes.
Remove the saucepan from heat. Whisk together the eggs, sesame oil, and 1/2 teaspoon salt, then pour the eggs into the hot broth in a slow stream, whisking constantly to scatter the eggs as they cook.
Stir in the spinach and let the leaves wilt briefly, then season the soup with salt to taste.
Serve the soup topped with 1 hard boiled egg per serving.