Step 1

Holding the chiles one at a time with metal tongs, quickly toast them by turning them an inch or two above an open flame for a few seconds until the aroma fills the kitchen. (Alternatively, toast chiles in a dry pan over medium heat, pressing them flat for a few seconds then flipping them over and pressing again.)

Step 2

When cool enough to handle, stem and seed the chiles, break them into pieces and put them in a blender along with tomatoes and their juice. (A food processor will work, though it won't completely puree the chiles.)

Step 3

Heat 2 tablespoons oil in a Dutch oven over medium heat. Add onion and garlic and cook, stirring frequently, until golden, 6 to 9 minutes. Scoop up the onion and garlic with a slotted spoon and transfer to the blender with the tomato mixture. Process until smooth.

Step 4

Return the pot to medium heat. When quite hot, add the puree and stir nearly constantly until thickened to the consistency of tomato paste, about 6 minutes. Add broth, water and epazote (if using). Bring to a boil, then adjust heat to maintain a simmer.

Step 5

Drain tofu, rinse and pat dry; cut into 1/2- to 3/4-inch cubes. Heat the remaining 2 teaspoons oil in a large nonstick skillet over medium heat. Add the tofu and cook in a single layer, stirring every 2 to 3 minutes, until beginning to brown, 6 to 8 minutes total. Add the tofu to the soup and simmer for 30 minutes.

Step 6

Add chard (or spinach or kale) to the soup and season with salt to taste, depending on the saltiness of the broth. Cook, stirring, until the greens are wilted, about 2 minutes, depending on the type of greens.

Step 7

Ladle the soup into 8 soup bowls. Divide avocado, tortilla chips and cheese (if using) among the bowls. Serve warm, with lime wedges.