In a medium saucepan, combine stock, sake, soy sauce, 1 tablespoon ginger and the garlic over medium heat.

Bring to a boil and simmer until reduced by half, 8 to 10 minutes.

Season with additional ginger, if desired.

Whisk in butter, if desired. (Sauce can be made up to 5 days ahead of time, but whisk in butter just before serving. Cover and refrigerate. Bring to a simmer before continuing.)

Brush fish fillets lightly with oil.

Sprinkle with salt and pepper.

Preheat broiler or prepare charcoal or gas grill.

Cook salmon, turning once and basting with some of the sauce, until fish looks almost opaque when the point of a knife is inserted into the thickest part, 3 to 4 minutes per side.

Bring remaining sauce to a simmer, and pour over cooked fish just before serving.

*Variation: Salmon can be baked instead of broiled or grilled. Preheat oven to 450°F and place fish in an oiled baking dish. Bake, basting once with sauce, until fish looks almost opaque when the point of a knife is inserted into the thickest part, 8 to 10 minutes.*