01 -
Heat a dry skillet over medium heat. Using tongs, press each dried chile flat onto the pan and hold for 15 to 20 seconds per side until the chile is fragrant and just pliable. Do not let them darken to brown or they will make the sauce bitter. Transfer to a plate as each one is done.
02 -
Place the toasted chiles in a small saucepan with 2 cups of chicken broth. Bring to a gentle boil over medium-high heat, then reduce heat to low and simmer for 12 to 15 minutes until the chiles are completely soft and press easily with the back of a spoon.
03 -
Transfer the softened chiles to a blender with 1 to 1.5 cups of the cooking liquid. Add the garlic, chopped onion, cumin, Mexican oregano, black pepper, and a pinch of salt. Blend on high for about 1 full minute until completely smooth. For a silkier texture, pour the mixture through a fine mesh sieve, pressing with a spoon.
04 -
In a wide skillet, warm the vegetable oil over medium heat. Add the flour and stir constantly for about 1 minute until the roux smells faintly nutty and turns a light golden color. Do not rush this step.
05 -
Carefully whisk the blended chile mixture into the roux in the skillet. It will spatter as it hits the hot roux, so stand back and whisk steadily. Add the remaining broth to reach your desired consistency. Simmer over medium-low heat for 10 to 12 minutes, stirring occasionally, until the sauce coats the back of a spoon.
06 -
Taste the sauce and add salt as needed. If it is too thick, stir in a splash of broth and heat through. If too thin, simmer uncovered for another 3 to 5 minutes. Use immediately or cool completely and transfer to an airtight container.