On a comal, over a mediumhigh heat, toast the chiles until fragrant, about 30 to 60 seconds dont burn them they will be bitter. Place in a bowl and Cover with the chicken stock and allow to soften, about 20 minutes. In a blender, place the chiles and stock. Blend until chopped. Add the garlic,onions, oregano, cumin, vinegar, and salt and pepper. Blend until very smooth. you may want to run it thru a sieve, to get the seeds out, At this point you may fry the sauce in 2 tablespoons of oil or lard, but this step is opptional if so,cook 10 min in the oil,otherwise just heat in pan for 10min. NOTE;you may want to make a roux with some flour and oil to thicken. Yield: about 3 cups