To make the marinade, add all of the marinade ingredients to a high powered blender and blend to a smooth consistency. Set aside.
Cut the flank steak into small strips against the grain. Place the steak strips in a bowl or shallow dish. Pour the marinade all over the steak and toss to coat.
Set the steak aside to marinate while you prep the remaining ingredients. Or, cover and refrigerate to marinate the steak for up to 24 hours.
When you are ready to cook the steak, prep the shallot and green onions as noted.
Heat a large non-stick skillet over medium heat and add sesame oil. Once hot, add in the shallot. Cook, stirring frequently for 2-3 minutes.
Add the beef strips into the skillet with the shallot. Pour in any remaining marinade also. Cook the beef, stirring occasionally, until all of the marinade juices thicken and begin to caramelize. The beef will be coated with the sauce and will absorb all of the sauce flavor. Remove the beef once the sauce has cooked down enough so it is just coating the meat pieces, about 10-15 minutes. *See recipe notes for alternate cooking instructions*
Serve immediately, topped with sliced green onions and sesame seeds.
If you don't like your beef cooked as noted, you can cook it for a shorter time, just 1-2 minutes on each side or until cooked to your liking. However, this method won't allow the sauce to caramelize like you see in the pictures above.
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