Place the chiles on a cookie sheet, and roast in a 350 degree oven until slightly toasted (when you can smell them, they're done). Remove from the oven, and slit open. Remove the seeds and veins, then cover the chiles with boiling water. Allow to sit for about 30 minutes. remove the chiles from the water (reserve water), and scrape the pulp from the chiles. Discard the skins (which can give the mixture a bitter flavor.) Return the chile pulp to the soaking water and reserve. Saute the garlic and onion in the lard until very soft but not browned. Stir in the flour, and the stock. Stir until thickened, then add the chile pulp mixture. Add the spices, and simmer until thickened. Place the mixture in a blender, and blend until smooth. Season to taste with salt. If you want a hotter mixture, add cayenne to taste.