Heat the pot: Set the Instant Pot to sauté and add the vegetable oil. Let it heat for about 1 minute until it shimmers slightly.
Sear the beef: Add the beef cubes in batches, searing each side for about 3 minutes until deep brown. Remove the beef and set aside on a plate.
Add aromatics: Add the garlic and ginger to the pot and stir for 30 seconds until fragrant, scraping up any browned bits from the bottom.
Build the sauce: Pour in the soy sauce, brown sugar, and beef broth, stirring to dissolve the sugar. Return the seared beef to the pot and stir to coat.
Seal and pressure cook: Close the lid, set the valve to sealing, and cook on high pressure for 20 minutes.
Release pressure: Let the pressure release naturally for 10 minutes, then carefully turn the valve to venting to release any remaining steam.
Make the slurry: While the pot rests, whisk the cornstarch and water together in a small bowl until smooth.
Thicken the sauce: Switch the pot to sauté, stir in the cornstarch slurry, and cook for about 2 minutes until the sauce thickens and coats the beef.
Finish with sesame oil: Turn off the pot and stir in the sesame oil for a toasted aroma.
Garnish and serve: Scatter sliced green onions over the beef and spoon it over hot steamed rice.
