I've seen versions that call for more mirin (a sweet Japanese cooking wine -- it's not something you'd ever actually drink, at least not the kind I've used, Kikkoman Aji-Mirin) than sake, but I'm a sucker for sake. After experimenting a little, I've settled on equal parts mirin and sake.
This sauce can be brushed on fish, shrimp, chicken, or beef while it's being grilled or broiled, and it's also great with vegetables. Whatever you're using it with, teriyaki sauce seems to go best on foods that cook quickly, as the sauce can burn near a flame. If you're using bigger cuts of meat or chicken on the bone, you can always start to brush the sauce on in the middle of cooking.
Makes a little more than 1 cup
3/4 cup mirin
3/4 cup sake
1/2 cup soy sauce
4 tablespoons plus 1 teaspoon sugar
1. Simmer mirin and sake in small saucepan over medium-low heat for 5 minutes.
2. Add soy sauce and sugar, stirring until sugar is dissolved, and cook over medium-low heat for 25 to 30 minutes. Sauce should maintain a slow, steady simmer and thicken just a bit by the time it's done.
3. Let sauce cool. It can be kept for a couple of weeks in the fridge.