Rinse, stem and seed the chiles, and place in a pot filled with water. Cover;
bring to a boil over medium heat, reduce heat, and simmer 20 to 30 minutes, until
Drain the cooked chiles and place them, along with the garlic and salt, in a
blender or food processor. Blend to a thick puree. Add the stock and blend for another
minute. Press the sauce through a fine sieve.