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1
Toast the New Mexican and guajillo chiles in a dry large cast-iron skillet over medium-high heat, turning, until warm and soft, about 30 seconds per side (do not let blacken, or the chiles will be bitter).
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2
Remove the chiles; reserve the skillet.
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3
Discard the stems; cut the chiles lengthwise with kitchen shears, and discard the seeds.
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4
Cover the chiles with boiling water.
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5
Let stand until hydrated, about 20 minutes.
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6
Meanwhile, cook the garlic and tomatoes in the skillet over medium-high heat, turning, until charred and soft, about 10 minutes.
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7
Set the tomatoes aside; peel the garlic.
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8
Heat the oil in the skillet over medium-low until hot but not smoking.
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9
Cook the onion until translucent, about 5 minutes.
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10
Add the chili powder; cook 1 minute.
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11
Drain chiles, reserving 1 1/2 cups liquid.
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12
Puree the onion, hydrated chiles, chipotle chiles, tomatoes, garlic, and oregano in a blender, adding a small amount of the reserved soaking liquid if the mixture seems dry.
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13
Pass the sauce through a fine sieve into the skillet.
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14
Cook over medium heat, stirring, 5 minutes.
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15
Add the remaining soaking liquid.
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16
Simmer until the sauce is thickened, 12 to 15 minutes.
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17
Season with salt.
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18
If not serving immediately, refrigerate up to 2 days; reheat over low (add water if the sauce seems too thick).
