Savory Beef and Onion Stir Fry with Umami Sauce

Ingredients

• 1 lb flank steak, thinly sliced
• 1 medium white onion, sliced and separated into layers
• 4 scallions, cut into 2-inch segments, whites and greens separated
• 4 cloves garlic, minced
• 1 tablespoon vegetable oil
• 1 tablespoon soy sauce
• 1 1/2 tablespoons cornstarch
• 2 teaspoons Shaoxing wine or rice vinegar
• 2 teaspoons sesame oil
• 1/2 teaspoon baking soda
• 1 tablespoon vegetable oil for marinade
• 1 tablespoon Shaoxing wine or rice vinegar
• 1 tablespoon oyster sauce
• 1/2 tablespoon dark soy sauce or regular soy sauce
• 1 teaspoon cornstarch
• 1/4 teaspoon black pepper
• 4 tablespoons cold water
• 1 teaspoon sugar