Make sauce: Rinse chiles and remove stems, then split open and discard seeds and ribs. Heat a dry well-seasoned cast-iron skillet or heavy skillet over moderate heat, then toast chiles in batches, turning them, about 30 seconds total. Transfer chiles to a heatproof bowl and pour boiling water over them. Cover bowl and soak chiles, stirring occasionally, until softened, about 20 minutes. Reserve 2 cups soaking liquid, then drain chiles in a colander.
Purée chiles, reserved soaking liquid, and roasted peppers in 2 batches in a blender until smooth (use caution when blending hot liquids). Force purée through a fine-mesh sieve into a bowl, pressing on and discarding solids. Cook garlic, cumin, oregano, and salt in butter in a 4-quart heavy saucepan over moderately low heat, stirring, 1 minute. Add flour and cook, stirring, 2 minutes. Whisk in chile mixture and simmer, whisking occasionally, until reduced to about 2 1/2 cups, 15 to 20 minutes. Add vinegar and salt to taste. Keep sauce warm, covered.
Grill steaks:Prepare grill for cooking. If using a charcoal grill, open vents on bottom of grill, then light charcoal. Charcoal fire is medium-hot when you can hold your hand 5 inches above rack for 3 to 4 seconds. If using a gas grill, preheat burners on high, covered, 10 minutes, then reduce heat to moderately high.
Pat steaks dry and season with salt. Grill steaks, uncovered, on lightly oiled grill rack, turning over once, 6 to 8 minutes total for medium-rare. Transfer to a platter and let stand, loosely covered with foil, 5 minutes. Serve steaks with sauce. Sauce can be made 1 week ahead and cooled completely, then chilled, covered. If you aren't able to grill, steaks can be cooked in batches in a hot well-seasoned ridged grill pan.
Copyright July 2003, Gourmet magazine. Printed with permission.
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