01 - Toss the sliced flank steak with 1 tablespoon cornstarch until evenly coated, ensuring each piece is lightly dusted for tender texture.
02 - Whisk together soy sauce, beef broth, brown sugar, sesame oil, minced garlic, fresh ginger, rice vinegar, and red pepper flakes in a medium bowl until sugar dissolves completely.
03 - Add the cornstarch-coated beef to the Instant Pot insert, then pour the sauce mixture over. Stir thoroughly to coat all beef pieces evenly.
04 - Seal the Instant Pot lid and ensure the steam release valve is set to Sealing. Select high pressure and cook for 10 minutes to tenderize the beef.
05 - Perform a quick pressure release, carefully open the lid, and add the broccoli florets to the pot, distributing them evenly throughout the beef mixture.
06 - Reseal the lid and cook on high pressure for 1 minute to blanch the broccoli to tender-crisp perfection. Quick release the pressure immediately.
07 - Mix 2 tablespoons cornstarch with 2 tablespoons cold water in a small bowl until smooth, then stir the slurry into the Instant Pot.
08 - Select Sauté mode and cook for 2 to 3 minutes, stirring constantly, until the sauce thickens and coats the back of a spoon. Serve immediately topped with sesame seeds and sliced green onions.