In a small bowl, whisk soy sauce, broth, mirin, brown sugar, and rice vinegar until the sugar dissolves.
Heat a small saucepan over medium.
Add 1 teaspoon neutral oil, then sauté garlic and ginger for 30–45 seconds until fragrant. Do not brown.
Pour in the soy mixture. Bring to a gentle simmer.
Stir in toasted sesame oil.
Simmer 2–3 minutes to let flavors meld.
In a cup, mix 1 tablespoon cornstarch with 1 tablespoon cold water until smooth.
Whisk the slurry into the simmering sauce. Cook 30–60 seconds until it lightly coats a spoon.
Turn off the heat and whisk in 1 teaspoon unsalted butter for a glossy finish.
Taste and adjust: more vinegar for brightness, more sugar for sweetness, or a splash of broth if it tastes too strong.
Add optional white pepper or chili oil if you like a little heat.
Hibachi-style veggies: Toss with sautéed zucchini, onions, mushrooms, and carrots.
Fried rice: Drizzle and toss at the end for shine and flavor.
Protein: Brush over grilled steak, chicken, shrimp, or tofu in the last minute of cooking.
Dipping: Serve warm as a dip for potstickers or skewers.
