Slice the flank steak against the grain into thin strips, about 1/4 inch thick. In a mixing bowl, combine with soy sauce, peanut oil, and 1 tablespoon of cornstarch. Marinate for 10 minutes.

In a separate bowl, whisk together chicken stock, Shaoxing wine, dark soy sauce, brown sugar, and remaining cornstarch until smooth. Set aside.

Steam broccoli florets in a skillet filled with boiling water for about 1 minute until bright green and slightly tender. Remove and set aside.

Increase heat and add peanut oil to the skillet. Add marinated beef and cook for 30 seconds until browned on one side. Flip and cook for another 1-2 minutes.

Stir in minced garlic and ginger. Cook for about 30 seconds until fragrant.

Return steamed broccoli to the skillet, pour sauce over, and stir everything together. Cook for about 1 minute until sauce thickens.