Simmer the sauce. Combine dark soy sauce, light soy sauce, vinegar, salt, and sugar in a small saucepan. Bring to a gentle simmer over medium heat, stirring until the sugar dissolves.
Add chili and finish. Mix in fresh or dried chili (if using) and cook briefly until the sauce thickens slightly. Remove from heat and adjust seasoning to taste.
Notes
Use the nutrition card in this recipe as a guideline.