In a saucepan combine all the ingredients (soy sauce, sake or water, brown sugar, rice vinegar, corn starch, and optional ginger).

Heat over medium-high heat, stirring or whisking to dissolve the brown sugar, and bring the teriyaki sauce to a simmer. Simmer for 1-2 minutes or until the sauce thickens.

Sauce should have the thickness to coat a spoon (it will thicken a little more as it cools) or continue simmer and thicken to your liking. For a thicker, more glaze like sauce, continue to simmer, stirring frequently, until it reaches your desired thickness. Set aside to cool and store in the fridge. Keeps for weeks if stored properly in the fridge.