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Add 3 tablespoons (45 ml) of soy sauce and 2 ½ tablespoons (37 ½ ml) of black vinegar to a small bowl. Use a whisk to stir the ingredients together until they’re completely mixed.  If you have celiac disease or a gluten-sensitivity, be sure to choose a soy sauce that is labeled “gluten-free.” Some contain wheat or other sweeteners and flavorings that contain gluten. You can usually find black vinegar at Chinese grocery stores or from online retailers. You can substitute Worcestershire sauce for the black vinegar if you prefer. When the soy sauce and black vinegar are fully mixed, add 2 tablespoons (25 g) of sugar to the bowl. Whisk the mixture until the sugar is fully incorporated. After the sugar is mixed into the dressing, add ½ teaspoon (3 g) of salt. Use the whisk to mix the dressing until the salt is completely blended in. You can adjust the amount of salt to taste.

Summary:
Combine the soy sauce and black vinegar. Mix in the sugar. Stir in the salt.