Skirt Steak

Boneless Skirt Steaks (AKA Philadelphia Steak and Arrachera Steak) are prized for their flavor. In fact, the cut is so rich and flavorful, it has been described as "butter in meat form."
It comes from the diaphragm, a muscle that is used with every breath the animal takes. This constant use gives the skirt steak its tremendous flavor, but heavily used muscles are typically less tender.
So, how to use it? This is the steak of choice for Philly Steak, fajitas, or stir frying, because these require cutting across the grain into thin strips that are inherently tender. If not cut into strips, it benefits from 24 hours of an acidic marinade to improve tenderness, and then can be served whole, as in Arrachera steaks, a popular Mexican dish.