Heat water to a boil and pour about 14 to 16 ounces of hot water into a glass. Submerge the dried chillies and allow them to sit for 20 – 45 minutes. Remove chilies from water, remove stems and seeds and save the chili flesh and the water they were soaking in. You will be using the water as a means of thinning out the sauce. You can also use 16 ounces of chicken or vegetable broth for this if you’d prefer.
Heat the oil in a skillet over medium to medium-high heat and sauté the onion until very soft and browned, about 15 to 20 minutes. Add the minced garlic and sauté another 5 minutes. Remove from heat and add the sautéed onion and garlic to a blender.
Heat the oven to 400 degrees. Cut the tomatoes in half and place them on a parchment or foil-lined baking sheet with the pasilla pepper. Roast tomatoes and pasilla pepper until skin is browned and begins pulling away from the soft flesh. Remove the stem and seeds from the pasilla pepper and add the pasilla pepper and tomatoes in the blender with the sautéed onion/garlic.
Place ALL ingredients (including tortillas) except for the cinnamon stick, the water the chilies were soaking in and the chocolate into the blender and blend until completely smooth. This may take a few minutes.
Pour the mixture into a large sauce pan and heat over medium. Add in the cinnamon stick, chocolate and pour a little of the water (or broth) into the sauce pan.
Stir until chocolate is melted and add more water.
Continue cooking the sauce at medium-low or medium heat (just below its boiling point), adding the water until there’s no more, and stirring periodically for 45 minutes.