In a small saucepan, whisk together the Tamari, 1/2 cup water, brown sugar, honey, rice vinegar, sesame oil, grated ginger, and minced garlic.
Place the saucepan over medium heat and stir until the sugar has completely dissolved.
In a separate small bowl, combine the cornstarch and 1 1/2 tablespoons of cold water, whisking until no lumps remain to create a slurry.
Bring the liquid mixture in the saucepan to a gentle boil over medium heat.
Slowly pour the cornstarch slurry into the saucepan while whisking constantly to prevent clumping.
Reduce the heat to low and simmer for 5 to 7 minutes, or until the sauce has thickened and coats the back of a spoon.
Remove the saucepan from the heat and allow the sauce to cool; it will continue to thicken and become glossier as its temperature drops.