Separate the strips of beef and ensure they aren’t clumped together. Season them with salt and pepper, then set aside.
In a medium bowl, combine the onion, garlic, broth, soy sauce, brown sugar, sesame oil, ginger, and red pepper flakes. Pour the mixture into the stainless steel liner of the Instant Pot.
Add the strips of beef, close the lid, and ensure the valve is set to sealing. Press the manual (pressure cook) button, then adjust the time to 5 minutes* (see note). After 5 minutes, allow a 5 minute natural release.
While the beef cooks, make the cornstarch slurry. Whisk together the cold water and cornstarch then set aside.
After the natural release, open the lid, and stir the contents. Press “Cancel” to turn off the “Keep Warm” function. Then, press “Saute.” Pour in the cornstarch slurry, and stir until the desired thickness is reached. Press, “Cancel” again, and stir in steamed broccoli.
Serve over rice or side of your choice.