Instructions:

• Begin by slicing the flank steak into ½-inch thick strips. This ensures that the beef cooks quickly and remains tender. For best results, slice against the grain. Once sliced, toss the beef in cornstarch until evenly coated.
• In a mixing bowl, combine the soy sauce, brown sugar, water, rice vinegar, minced garlic, and minced ginger. Whisk these ingredients together until the sugar is dissolved. Set aside a small bowl to prepare the cornstarch slurry by mixing 1 tablespoon of cornstarch with 2 tablespoons of water.
• Heat the vegetable oil and sesame oil in your skillet over medium-high heat. Once hot, add the beef strips in a single layer. Cook for about 2-3 minutes on each side, or until the beef is browned and cooked through. Remove the beef from the skillet and set it aside.
• In the same skillet, pour the prepared teriyaki sauce mixture. Bring it to a simmer and allow it to cook for 2-3 minutes. Then, stir in the cornstarch slurry and cook for an additional minute or until the sauce has thickened.
• Return the cooked beef to the skillet and toss it in the teriyaki sauce, ensuring each piece is well-coated. Allow it to heat through for another minute. Serve over steamed rice, noodles, or alongside stir-fried vegetables.