Flat-iron steak is on sale at my grocery store. How should I cook it?
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The second-most tender muscle of the cow combined with the full flavor of the chuck primal, it's my favorite cut. Use it any way you'd use tenderloin -- grill it and slice it into strips for Steak Frites or a tomato beef salad, make it into Stroganoff or Hungarian stew or a big pot of Chili con Carne. On sale, load up the freezer!
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As ChefOno noted hanger steak is great on the grill especially over a real wood charcoal fire. Shamless plug, go to "Features" and select "Not recipes" and you will see my tips on grilling steak. For hanger steak I would think about cooking to an internal temperature not much over 120F. And for God's sake don't flip it.