In a small bowl or liquid measuring cup, combine the soy sauce, sake or rice vinegar, dark sesame oil, toasted sesame seeds, sugar, minced garlic, and grated ginger.
Whisk vigorously until the sugar is completely dissolved into the liquid.
Stir in the minced scallions.
Use immediately as a dipping sauce or marinade, or transfer to an airtight container and refrigerate for up to 2 days for the flavors to meld even more.
For the Tahini Soy Variation
In a small bowl, combine 1/2 cup (480 ml) soy sauce, 2 tablespoons dark sesame oil, 1 tablespoon (15 ml / 0.5 fl oz) sugar, and 2 minced garlic cloves from the main recipe.
Substitute the sake with 1/4 cup (960 ml) mirin or honey and the toasted sesame seeds with 1/4 cup (960 ml) tahini. Omit the ginger and scallions.
Whisk everything together until smooth and creamy. This version is fantastic with steamed eggplant.
Add a pinch of red pepper flakes for heat, if desired.
While you can use this sauce immediately, its flavor deepens and becomes more complex if you let it rest in the refrigerator for at least 30 minutes before serving.