Like guacamole, tortilla soup has a place, I feel, in practically every collection of Mexican recipes. It’s a filling, flavorful meal that can be made with little effort, but one that sings with an unmistakable Mexican harmony. Earthy dark pasilla chile. The softening crunch of toasty corn tortillas. Soul-satisfying broth. And creamy-rich avocado and cheese.
A note about pasilla (sometimes called negro) chile: Its unique flavor defines tortilla soup in central Mexico. In Michoacan, it’s ancho chile. In your kitchen, it might turn out to be another chile, like New Mexico or even a little smoky chipotle (be forewarned that chipotle will make the broth quite spicy). Though for these everyday recipes I’ve relied heavily on the easier-to-use powdered dried chile, finding powdered pasilla (negro) can be harder than finding the whole pod. Should powdered chile be at your finger tips (be it powdered pasilla (negro), ancho or beyond), add about 1 tablespoon to the pan about halfway through the cooking of the onion.
In Mexico, it’s more common to crush toasted chile pods over the soup than to add it to the base. You can follow that lead, or do both as we do in our restaurants.
Quickly toast the chile by turning it an inch or two above an open flame for a few seconds until its aroma fills the kitchen. (Lacking an open flame, toast it in a dry pan 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 the tomatoes with their juice. (A food processor will work, though it won’t completely puree the chile.)
Heat the oil in a medium (4-quart) saucepan over medium-high. Add the onion and garlic and cook, stirring frequently, until golden, about 7 minutes. Scoop up the onion and garlic with a slotted spoon, pressing them against the side of the pan to leave behind as much oil as possible, and transfer to the blender. Process until smooth.
Return the 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 epazote, if using. Reduce the 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).
Just before serving, add the chicken to the simmering broth. Divide the avocado, cheese and tortilla chips between serving bowls. When the chicken is done, usually about 5 minutes, ladle the soup into the bowls. Garnish with the crema. Pass the lime separately.