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1
Rinse chiles and remove stems, then split open and discard seeds and ribs.
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2
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.
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3
Transfer chiles to a heatproof bowl and pour boiling water over them.
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4
Cover bowl and soak chiles, stirring occasionally, until softened, about 20 minutes.
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5
Reserve 2 cups soaking liquid, then drain chiles in a colander.
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6
Puree chiles, reserved soaking liquid, and roasted peppers in 2 batches in a blender until smooth (use caution when blending hot liquids).
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7
Force puree through a fine-mesh sieve into a bowl, pressing on and discarding solids.
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8
Cook garlic, cumin, oregano, and salt in butter in a 4-quart heavy saucepan over moderately low heat, stirring, 1 minute.
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9
Add flour and cook, stirring, 2 minutes.
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10
Whisk in chile mixture and simmer, whisking occasionally, until reduced to about 2 1/2 cups, 15 to 20 minutes.
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11
Add vinegar and salt to taste.
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12
Keep sauce warm, covered.
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13
Prepare grill for cooking.
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14
If using a charcoal grill, open vents on bottom of grill, then light charcoal.
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15
Charcoal fire is medium-hot when you can hold your hand 5 inches above rack for 3 to 4 seconds.
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16
If using a gas grill, preheat burners on high, covered, 10 minutes, then reduce heat to moderately high.
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17
Pat steaks dry and season with salt.
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18
Grill steaks, uncovered, on lightly oiled grill rack, turning over once, 6 to 8 minutes total for medium-rare.
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19
Transfer to a platter and let stand, loosely covered with foil, 5 minutes.
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20
Serve steaks with sauce.
