Place the roasted chiles in a plastic or brown paper bag and let rest 10 minutes. Peel, seed, and chop 5 of the chiles, reserving 1 for garnish.
Place the chopped chiles in a blender or food processor fitted with the steel blade. Puree with the onion, garlic, and ½ cup of the chicken stock. Set aside.
Heat the oil in a medium-size saucepan over medium-high heat until it begins t