⅛teaspoonred pepper flakes or pinch of cayenneoptional
Instructions
In a small bowl, combine the salt, chile powder, cocoa, brown sugar, coriander, and garlic. Pat steaks dry with a paper towel, then rub with spice mixture. Transfer steaks to a large resealable bag and refrigerate for 6 hours, or up to 24 hours. (You can skip the refrigeration time, if you need to, but the steaks may not be as tender.)
For a gas grill, preheat on high for about 15 minutes. Clean and oil cooking grates, then turn burners to medium-high.
Brush the steaks with oil. Place them on the hot grill and cook until charred on both sides, about 3-5 minutes per side, or until internal temperature reaches 135 degrees F (for medium-rare). Transfer steak to a carving board, tent loosely with foil, and let rest for 10 minutes.
Meanwhile, make the cowboy butter by whisking together the ingredients in a small bowl.
Slice the steak thinly going against the grain. Serve with cowboy butter, if desired.
Notes
If you like a little more heat, increase the chipotle chile powder up to 1 tablespoon.