Heat oil in large sauté pan or skillet until just smoking. Add beef in single layer being sure not to overfill pan or it will steam instead of sear. Cook in two batches if necessary. It shouldn’t take longer than 1-2 minutes to brown.
Flip and brown other side. TURN OFF BURNER and then remove beef to plate. If you are using an electric stove, move pan to an unused burner.
Add oils, ginger and garlic to pan stirring quickly to make sure it doesn’t brown. It will depend on how hot your pan is.
Add brown sugar and soy sauce and stir until bubbly. If not bubbling, you can turn heat back on to medium.
Add water/cornstarch, stir in completely and cook until bubbly and then for about 30 seconds.
Add beef and any juices on plate back to pan and stir until nicely coated.
Sprinkle with sesame seeds and serve.