The Food Lab: Better Home Cooking Through Science

The meat itself should be ultra-juicy, with an
overwhelming, almost buttery beefiness—this is skirt steak,
after all, the butteriest of all beef—accented by a marinade
that is slightly sweet, very savory, and packed with lime and
chili. While fajitas are traditionally made with outside skirt—
part of the diaphragm muscle of the steer—the cut is pretty
much unavailable unless you work for a restaurant that
special orders it. At the butcher or meat counter, you’re far
more likely to find inside skirt, which will do us just fine.