In a bowl, toss sliced beef with soy sauce, cornstarch, and oil. Set aside for 10 minutes.
Blanch broccoli in boiling water for 30–60 seconds until bright green. Drain and set aside.
Heat 1 tablespoon oil in a wok or large skillet over high heat. Sear beef in a single layer until browned. Remove and set aside.
Add remaining oil to the pan. Sauté garlic and ginger for 15–20 seconds until fragrant.
In a bowl, whisk together all sauce ingredients. Pour into the pan and stir until thickened.
Return beef and broccoli to the pan. Toss until evenly coated in sauce.
Remove from heat and serve immediately.