Whisk together all the marinade ingredients in a small bowl. Place the flank steak in a shallow dish (like a 9X13-inch pan) and pour the marinade over the steak. Cover and let marinade for 8-10 hours, flipping the steak once or twice during the marinade time.
Grill the flank steak over medium heat for about 7-8 minutes per side, depending on how well done you like your steak. Let the steak rest for about 10 minutes before slicing very thinly against the grain and serving.
Notes
Freezable: Julia, who sent me the recipe (thanks, Julia!) said she keeps a few of these marinating flank steaks in the freezer to thaw and grill as needed. Great idea! Put the marinade and steak in a freezer bag, press out the air and freeze. Thaw overnight in the refrigerator and then grill. Flank Steak: also, if you are using flank steak a few ounces either direction from the 2 pounds listed in the recipe, you should be fine without having to increase or decrease the marinade ingredients - otherwise adjust accordingly to the size of meat you are using.