Chile Puree: Preheat broiler. On sheet tray arrange chiles in single layer. Place under broiler and cook 15 seconds. Remove and turn chiles. Cook 15 seconds on other side. Place chilies in bowl with hot tap water to cover. Soak 30 to 40 minutes. Strain and place chilies in blender. Purée chiles, adding just enough broth to help mixture through blades. Pass mixture through medium-fine strainer.
Heat oil in 1-quart saucepan over medium heat. Add onion and sauté until golden brown. Add garlic and cook 1 minute. Add Chile Purée and bring to boil. Reduce heat and simmer, reducing Purée to thick paste, being careful not to burn. Add tomato Purée and chicken broth. Bring to boil. Reduce heat and simmer, covered, 20 to 30 minutes. Season to taste with salt.
Garnish soup as desired with Mexican cheese, avocados, sour cream, lime wedges, corn tortilla and chile strips.Makes 4 3/4 cups Source: