In a cold pan, whisk together the cornstarch and water, then mix in all of the rest of the sauce ingredients. Bring to a boil and simmer for a 2-3 minutes to thicken. It might be hard to see that it's getting thick, but you can tell because the bubbles start rolling more slowly. Remember that it will thicken even more as it cools, so don't overcook!
You can stir in a tablespoon of sesame seeds at this point, if you want. Use now or refrigerate for up to a week.
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Notes
Store for up to a week in the fridge or up to 6 months in the freezer. Whisk or shake before using.This recipe yields approximately 2 cups of teriyaki sauce. 1 serving = 2 tablespoons