1/2 cup ketchup
1/3 cup rice vinegar or white vinegar
1/4 cup sugar
2 tablespoons soy sauce
1 tablespoon cornstarch
2 tablespoons water
Mix ketchup, vinegar, sugar, and soy sauce in a saucepan
Stir cornstarch and water together in a small bowl until smooth
Heat the saucepan over medium heat
Add the cornstarch mixture to the saucepan
Stir constantly until the sauce thickens
Remove from heat and use warm or cool before serving