Sizzling Chinese Pepper Steak with Onions

1 tablespoon rice vinegar

1 teaspoon sugar

1 tablespoon cornstarch mixed with 2 tablespoons water (cornstarch slurry)

1/4 teaspoon black pepper

1/4 teaspoon red pepper flakes (optional, for extra heat)

Cooked white rice or steamed rice, for serving

Instructions:

Marinate the Steak:

In a medium bowl, combine the soy sauce, cornstarch, and vegetable oil. Add the thinly sliced flank steak and toss to coat. Let marinate for at least 15 minutes.

Prepare the Stir-Fry Sauce:

In a small bowl, whisk together the bee