3/4cupdark brown sugar,you can use light brown sugar instead
1/2cuplow sodium beef broth
1teaspoonminced fresh ginger
1/2teaspooncrushed red pepper flakes
Cut flank steak against the grain into thin slices. Cut longer slices in half so that they are bite-sized.
Place flank steak slices in a medium bowl and add cornstarch. Stir until evenly coated. Let sit 10 minutes.
Make the sauce. In a medium bowl, stir together soy sauce, brown sugar, beef broth, vinegar, sesame oil, ginger, garlic, and crushed red pepper flakes.
Turn Instant Pot to "Saute" mode. Add 1 tablespoon of oil and when hot, sear flank steak in batches until browned on both sides. Add more oil if needed between batches. Be sure not to crowd the flank steak. Hit "Cancel" on the Instant Pot.Note: If you'd rather, you can sear the flank steak in a large skillet.
Return all flank steak to the Instant Pot. Pour sauce over it. Place lid on and set to Manual (High Pressure) for 10 minutes. Be sure the valve is in sealing position.
When time is up, do a quick pressure release.
Stir in green onions. Sprinkle with sesame seeds and serve with rice.
For easier slicing, place flank steak in the freezer for 30 minutes before slicing.