In a saucepan combine the soy sauce, ¼ cup of water, brown sugar, mirin, sesame oil, rice wine vinegar, black pepper, red pepper flakes, sriracha, ginger, garlic, and scallion. Heat the sauce on high and bring to a boil, about 5-7 minutes
In a small bowl, combine the 3 tablespoons of water and cornstarch until smooth. Once the sauce is boiling, add the cornstarch slurry and whisk until thick. Continue to cook the sauce until it is thick enough to coat the back of a spoon and hold, about 6-8 minutes.
Let the sauce cool completely before pouring into a clean jar. The sauce is ready if you would like to use it immediately as well. Store remaining sauce in an airtight container for up to two weeks.
