After my firm proclamation of skirt steak being one of the greatest steaks known to man, I inevitably got some questions and challenges to that. As comments rolled in, I realized that I've been so skirt-heavy in recent years that my recollection of other cuts, primarily flank, was a bit hazy. Only one way to correct that: grill more steaks!
After using half of my Mojo sauce as a dip for tostones (fried plantains) and fried yucca, I used the other half as a marinade for a two-pound piece of flank steak. I let the meat marinate in the sour, acidic Mojo for just an hour, then grilled it up alongside some onions. Once medium-rare, the steak rests, then we sliced and dug in.
Now don't get me wrong, this was a pretty awesome steak—beefy and tender with a slight tang from the Mojo—but it was only reaffirming my allegiance to skirt. For all the great flavor going on, I knew skirt would deliver even more, and kind of wished I was eating that. Flank will do no wrong here, but you can change up the cut for skirt easily, if you really want to raise the steaks.
Season steak liberally with salt and pepper. Place steak in a large resealable bag and pour in Mojo sauce. Seal bag, removing as much air as possible, and toss to evenly coat steak in sauce. Let marinate for 1 hour at room temperature.
Light one chimney full of charcoal. When all the charcoal is lit and covered with gray ash, pour out and arrange the coals on one side of the charcoal grate. Set cooking grate in place, cover grill and allow to preheat for 5 minutes. Clean and oil the grilling grate. Remove steak from marinade and pat dry. Place steak on hot side of the grill and cook until well seared on both sides, about 3 minutes per side. Move to the cool side of the grill, cover, and continue to cook until the center of the steak registers 125°F on an instant-read thermometer for medium-rare, or 135° for medium. Transfer to a cutting board and let rest for 10 minutes.
While steak is resting, brush onion slices all over with olive oil and season with salt. Place over the hot side of the grill and cook until softened and charred, about 3 to 5 minutes per side. Remove to cutting board.
Carve steak against the grain into 1-inch slices and serve with grilled onions.