Using tongs, hold chilies over a gas flame to toast, or put under a broiler.
Do not burn.
Remove stems, shake out seeds, cover with water, and bring to a boil.
Let stand for 20 minutes.
Put in a blender with the water and whirl until smooth; or grind chilies and press through a strainer, then combine with water.
Whirl tomatoes in blender or press through a strainer.
Mash garlic and combine all ingredients.
Simmer for 15 to 20 minutes.
This sauce may be thickened slightly with 1 1/2 tablespoons each of butter and flour.