Marinate the beef. In a bowl, toss sliced steak with 2 tablespoons soy sauce and 1 teaspoon cornstarch. Let it marinate for at least 15 minutes (up to 1 hour) while you prep the vegetables.
Make the sauce. In a small bowl, whisk together soy sauce, beef broth, cornstarch, honey, garlic, ginger, and black pepper. Set aside.
Cook the beef. Heat 1 tablespoon oil in a large skillet or wok over medium-high heat. Add beef in a single layer, cooking 1–2 minutes per side until browned but not fully cooked through. Remove to a plate.
Cook the vegetables. Add remaining oil to the pan. Stir-fry onion and bell peppers for 3–4 minutes, until just tender-crisp.
Bring it all together. Return beef to the pan. Stir the sauce once more and pour it in. Toss everything together and simmer 2–3 minutes, until the sauce thickens and the beef is cooked through.
Serve. Serve hot over steamed rice or noodles. Garnish with sesame seeds or green onions if desired.
Notes
Slice against the grain – I always make sure to cut the beef thinly across the grain. Cutting the beef thinly across the grain shortens the muscle fibers, making it much more tender.
Don’t skip the quick marinade – Even if I’m in a rush, I give the beef at least 15 minutes in soy sauce and cornstarch. It’s such a simple step, but it really transforms the texture into that silky, restaurant-style finish we all love.
Use high heat – I’ve learned that a hot skillet is non-negotiable. The beef sears beautifully without overcooking, and the veggies stay crisp and bright.
Cook in batches if needed – Crowding the pan steams the meat; work in batches so it browns properly.
Keep veggies crisp-tender – Stir-fry just until the peppers are bright and slightly softened; they should keep some crunch. Nobody likes mushy or overcooked peppers.
Adjust sauce consistency – If your sauce thickens too much, add water a tablespoon at a time until glossy and smooth.
* Instead of flank steak, you can also use skirt steak, sirloin steak, ribeye.