Slice the flank steak thinly against the grain into strips about 1/8–1/4 inch thick. Cutting against the grain shortens the muscle fibers and makes the cooked steak noticeably more tender. For easier slicing, chill the steak in the freezer 10–15 minutes so it firms up.

Lightly toss the sliced steak with 1/2 tsp cornstarch and a pinch of black pepper (reserve the rest of the cornstarch). The cornstarch lightly coats the meat and helps it brown while creating a silky sheen when combined with the sauce later.

If you have time, toss the steak with 1 tablespoon of the stir-fry sauce and let it sit 8–10 minutes at room temperature. This brief marinade seasons the meat and begins to tenderize it; because the sauce will be cooked, it’s safe to use it in the marinade and the pan.

Prepare the rice (if not already cooked) and the vegetables: cut bell pepper into 1/2-inch strips, break broccoli into small florets, and slice carrot thinly (diagonal slices cook faster). Uniform pieces ensure even cooking and a pleasing mouthfeel.

Heat a large wok or heavy skillet over high heat until very hot (you should see a faint shimmer). High heat is essential for a proper stir-fry: it sears the meat quickly, preventing it from stewing and helping the vegetables remain crisp-tender.

Add the vegetable oil and swirl to coat. When the oil is just smoking, add the steak in a single layer. Do not overcrowd the pan—sear in batches if necessary. Let the strips sit undisturbed for 30–45 seconds to develop a deep, caramelized crust, then stir-fry for another 60–90 seconds until just browned but still medium-rare to medium (it will finish cooking later). High-heat searing locks in juices and creates flavor via the Maillard reaction.

Transfer the seared steak to a plate and immediately wipe out the pan if there’s excessive char (leave a thin coating of fond). Return the pan to high heat and add another drizzle of oil if needed. Add the minced garlic and stir 10–15 seconds to bloom its aroma—browning it gently releases flavor but avoid burning, which turns bitter.

Add the mixed vegetables to the pan and stir-fry 2–3 minutes until the carrots begin to soften and broccoli turns bright green. Stirring constantly over high heat cooks the vegetables quickly so they keep a bright color and crunchy texture.

Return the steak to the pan. Mix the remaining 1 1/2 tsp cornstarch (from the reserved amount) with the remaining 1 tablespoon of stir-fry sauce and 2 tablespoons of water to form a slurry; pour this around the edge of the pan. Toss everything together over high heat for 30–60 seconds until the sauce thickens to a glossy coating. The cornstarch slurry creates a clingy sauce that coats meat and veg evenly.

Taste and adjust: add a pinch of salt or a splash more sauce if it needs brightness, and a grind of pepper. Remove from heat and let rest 1 minute so the sauce settles—this keeps the steak juicy.

Serve the stir-fry over the warm jasmine rice, garnish with sliced scallion and an optional squeeze of lime. The hot rice soaks up the savory sauce and provides a fragrant, slightly sticky base.