Add all of the ingredients for the steak marinade to a mixing bowl. Whisk the ingredients together until combined. Set aside.

Next, place the flank steak onto a cutting board and season it with 1 teaspoon of kosher salt. Massage the salt into the steak. Cover it with a piece of parchment paper. Use a meat tenderizer to pound the flank steak so that it is an even thickness (~1.5-2 inches thick).

Transfer the steak to a baking dish or a quart-sized plastic bag. Pour the marinade over the steak and massage the marinade into the steak. Place in the refrigerator for at least 2 hours or overnight.

Remove the meat from the refrigerator and allow the steak to sit at room temperature for 20-30 minutes before searing.

Sear the steak. Heat the remaining olive oil in a large cast iron skillet. When the olive oil is hot, add the flank steak and sear for 3-4 minutes on each side or until the internal temperature is 135ºF for medium rare. Remove from the skillet and let the flank steak rest for 10 minutes before slicing.