How do I prepare arrachera (Flank Steak) like they do in Mexico?

I just came back from Mexico, and I had steak a few times. The best I had was the Arrachera cut which the cook told me is what we call "Flank Steak" in the U.S. I know flank steak to be very tough, but in Mexico it was like butter. The cook told me that the meat is so soft because it is tenderized and... show more I just came back from Mexico, and I had steak a few times. The best I had was the Arrachera cut which the cook told me is what we call "Flank Steak" in the U.S.

I know flank steak to be very tough, but in Mexico it was like butter. The cook told me that the meat is so soft because it is tenderized and marinaded and that's what makes it so soft. Unfortunately, I didn't ask him exactly how it's marinaded and tenderized.

I just came back from Costco with a HUGE Flank steak but I realize that If I don't marinade and tenderize it it will be like eating leather.

Does anyone know how to prepare this flank steaks so I can get the same great results they do in Mexico?
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