Tortilla soup has a place in nearly every collection of Mexican recipes. Also known as Sopa Azteca, this soup is served with tender chunks of chicken, blended with tangy chipotle sauce and topped with fresh avocado.
Toast chile in a dry skillet over medium heat, pressing it flat for a few seconds, then flipping it over and pressing it again. Break the chile into pieces and put in a blender jar along with tomatoes and adobo sauce.
Heat the oil in a medium-size (4-quart) saucepan over medium-high. Add the onion and garlic and cook, stirring frequently, until golden, about 7 minutes. Use a slotted spoon to transfer onion and garlic to the blender. Process until smooth puree.
Return the oily pan to medium-high heat. When quite hot, add the puree and stir nearly constantly, until thickened to the consistency of tomato paste, about 6 minutes. Add the broth and cilantro sprigs. Heat mixture to a boil. Reduce heat to medium-low and simmer for 15 minutes. Taste and season with salt, usually about a generous teaspoon (depending on the saltiness of the broth).
Divide the avocado, cheese, and tortilla chips between 6 serving bowls. Just before serving, add the chicken to the simmering broth to warm it, about 3 minutes. Ladle the soup into the prepared bowls. Drizzle with the crema. Pass the lime separately.