Mix 1 tablespoon cornstarch with 1 to 2 tablespoons cold water
Stir until completely smooth
Bring the soup to a gentle simmer
Slowly pour in the cornstarch slurry while stirring
Let the soup cook for 1 to 2 minutes
Add more slurry if a thicker consistency is needed
Stir well after each addition
Avoid adding cornstarch directly to hot soup
Do not boil vigorously after adding cornstarch