Step 1: Prepare the Ingredients
Slice the flank steak thinly against the grain and toss it with 1 tsp soy sauce and 1 tsp cornstarch. Let it marinate for 15 minutes.
Cut the broccoli into bite-sized florets. If using frozen broccoli, thaw and pat dry to remove excess moisture.
In a small bowl, whisk together all the stir-fry sauce ingredients until smooth.
Step 2: Cook the Beef
Heat 1 tbsp oil in a large skillet or wok over medium-high heat.
Add the beef in a single layer and sear for 1-2 minutes without stirring.
Stir and cook for another 1-2 minutes until browned. Remove the beef from the pan and set aside.
Step 3: Cook the Broccoli
In the same pan, add 1 tbsp oil and the broccoli. Stir-fry for 2-3 minutes until bright green and slightly tender.
Remove from the pan and set aside.
Step 4: Combine Everything
Pour the stir-fry sauce into the pan and stir for 1-2 minutes until it thickens.
Return the beef and broccoli to the pan, tossing to coat everything in the sauce.
Simmer for 1 more minute, then remove from heat.
Step 5: Serve & Enjoy
Garnish with sesame seeds and chopped green onions if desired.
Serve hot over steamed rice, brown rice, or noodles.