2 tablespoons brown sugar
1 1/2 tablespoon finely ground Allegro Espresso Sierra or other dark coffee
2 teaspoons chili powder
1/8 teaspoon cayenne
2 teaspoons kosher salt
2 1/2 pounds flat iron steaks, each 1 1/4 pounds
1 very large or 2 or more smaller cedar planks for grilling, soaked in water at least 3 hours
2 teaspoons extra-virgin olive oil, plus more for oiling planks
Combine sugar, coffee, chili powder, cayenne and salt. Cut steak to fit on cedar planks if necessary. Brush steak with 2 teaspoons oil; sprinkle all over with coffee rub and press to adhere. Set aside.
Prepare a grill for high-heat cooking. When very hot, bank coals on one side of grill, leaving one side free of coals; if using a gas grill, turn burner off on one side. Have a spray bottle filled with water handy. Heat cedar planks on cool side of grill for 3 minutes; remove from grill, brush one side lightly with oil and set aside.
Grill steaks on hot side of grill until just seared, 1 to 2 minutes per side. Transfer steaks to oiled sides of planks and place planks near (but not over, if possible) hot zone on grill; close grill cover and cook until steaks reach desired doneness, 8 to 12 minutes for medium-rare. Spray edges of planks with water if they catch fire. Remove planks from grill; rest steaks on planks 10 minutes before slicing.