Slice and Marinate the Beef (5 mins)
Slice flank steak thinly against the grain. In a small bowl, toss the beef with 1 tbsp soy sauce, 1 tsp cornstarch, and a drizzle of sesame oil. Set aside.
Make the Stir Fry Sauce (2 mins)
Whisk together soy sauce, beef broth, brown sugar, oyster sauce, rice vinegar, sesame oil, cornstarch, and red pepper flakes.
Cook the Broccoli (3 mins)
Heat 1 tbsp oil in a large skillet or wok over medium-high heat. Add broccoli florets and a splash of water; stir fry 2–3 minutes until bright green but crisp. Remove and set aside.
Cook the Beef (5 mins)
In the same pan, add remaining oil. Add beef in a single layer, sear for 1–2 mins, then stir. Add garlic and ginger; stir fry until beef is cooked through.
Add the Sauce and Broccoli (5 mins)
Return broccoli to pan, pour in sauce, and stir. It’ll bubble and thicken in about 1–2 mins. Taste and adjust.
Serve and Garnish (2 mins)
Remove from heat, garnish with green onions if you like, serve over rice, and enjoy!