In a small bowl, combine ½ cup of the chicken broth and the cornstarch to create a slurry.
In a pot, bring the remaining chicken broth, garlic clove, ginger slice, and the whites of the green onions to a boil over medium-high heat. Stir in the cornstarch mixture. Reduce the heat to a simmer.
Slowly pour in the beaten eggs in a thin stream (*see note) while stirring the soup. Once the eggs are added, bring just to a boil and remove from the heat.
Discard the ginger and garlic clove. Top with green onions and crushed red pepper flakes (if using).
