In a small bowl, whisk soy sauce, chicken broth, brown sugar, and 1 Tbsp corn starch.
In a separate bowl, toss steak with remaining corn starch.
In a large cast-iron skillet, heat 2 Tbsp canola oil over medium-high heat. Add steak and cook, turning only once, until browned; about 6-8 minutes. Transfer to clean plate.
Heat remaining canola oil and add broccoli florets. Cook, stirring occasionally until slightly tender; about 3-4 minutes.
Add scallions, ginger, garlic; stir to combine; cook for 1 minute until fragrant.
Add steak, along with sauce mixture, to pan and stir to combine. Cook, heating steak through, for 1-2 minutes until sauce thickens slightly.
Remove from heat and serve immediately over rice and garnished with additional sliced scallions and sesame seeds.