In a bowl, toss the sliced flank steak with 1 tbsp soy sauce, 1 tbsp cornstarch, and 1 tbsp vegetable oil until evenly coated. Let sit at room temperature for 10 minutes while preparing other ingredients.

In a small bowl, whisk together beef broth (or water), 1/4 cup soy sauce, brown sugar, hoisin sauce, 1 tbsp cornstarch, and sesame oil until the cornstarch dissolves. Set aside.

Heat 1 tbsp vegetable oil in a large skillet or wok over high heat. Add broccoli florets and 2 tbsp water. Cover and steam for 2-3 minutes until crisp-tender and bright green. Transfer to a plate.

Add the remaining 1 tbsp oil to the pan. Spread the marinated beef in a single layer (work in batches if needed) and sear without moving for 1-2 minutes per side until browned but not fully cooked through. Remove and set aside with the broccoli.

Reduce heat to medium. Add minced garlic and ginger to the pan; stir-fry for 30 seconds until fragrant.

Return the beef and broccoli to the pan. Pour in the prepared sauce and toss everything together. Cook for 1-2 minutes, stirring constantly, until the sauce thickens, the beef is no longer pink, and reaches an internal temperature of 145°F (63°C), and evenly coats the beef and broccoli.

Remove from heat and pile over steamed jasmine rice. Garnish with sliced green onions and sesame seeds.