In a medium saucepan combine the brown sugar, tamari, water, chili paste, rice wine vinegar, sesame oil, black pepper, ginger and garlic. Heat on high and bring to a boil.
Meanwhile, in a small bowl, combine the cornstarch and water until smooth.
Once the sauce is at a boil, whisk in the cornstarch slurry and reduce the heat to simmer until thick.
Let cook before transferring to a jar or container to store it. You can store it for up to three weeks.