Combine Base Ingredients: Mix white sugar, apple cider vinegar, ketchup, and soy sauce in a saucepan over medium heat.
Prepare Cornstarch Mixture: Whisk cornstarch and water in a separate bowl to create a smooth mixture.
Thicken the Sauce: Slowly add the cornstarch mixture to the base ingredients while stirring continuously until the sauce thickens.
Finalize the Sauce: Cook on low heat until the sauce reaches a rich, glossy consistency.
Cooling and Storage: Allow the sauce to cool, then transfer to a container for refrigeration.
