Slice the beef: Freeze the steak for 15–20 minutes to firm it up. Slice thinly against the grain into bite-size strips. Pat dry with paper towels.

Whisk the sauce: In a bowl, combine soy sauce, oyster sauce, rice vinegar, brown sugar, cornstarch, broth, sesame oil, red pepper flakes (if using), and black pepper. Whisk until smooth.

Marinate the beef: Add half of the sauce to the sliced beef, toss to coat, and let sit for 10–15 minutes while you prep the broccoli. Reserve the remaining sauce.

Prep the broccoli: Cut broccoli into small florets. Peel and slice the stalk if you like—it's tender and tasty when thinly sliced.

Par-cook the broccoli: Heat 1 tablespoon oil in a large skillet or wok over medium-high. Add broccoli and a splash of water. Stir-fry 2–3 minutes until bright green and crisp-tender. Transfer to a plate.

Sear the beef: Add another tablespoon of oil to the hot pan. Lay the beef in a single layer. Cook 1–2 minutes per side until browned but not fully cooked through. Work in batches to avoid overcrowding. Transfer to the plate with broccoli.

Sauté aromatics: Reduce heat slightly if needed. Add a little more oil if the pan is dry. Stir in garlic and ginger for 30 seconds until fragrant—don’t let them burn.

Bring it together: Return broccoli and beef (plus any juices) to the pan. Pour in the reserved sauce. Toss over medium-high heat for 1–2 minutes until the sauce thickens and everything is glazed.

Taste and adjust: Add a splash of water if the sauce is too thick, or a dash of soy for more salt. Finish with green onions and sesame seeds if using.

Serve: Spoon the stir‑fry over warm rice. Eat immediately for the best texture.