Step 1

Toast the chiles. If you have a gas stove, you can hold them with tongs over the flame one at a time for a few seconds until fragrant. But if like me you use an electric stove, put them in a dry skillet over medium heat and press them flat for a few seconds on each side. (See Notes below for using chile powder instead.)

Step 2

When the chilies are cool enough to handle, stem and seed them, tear them into pieces, and put them in a blender along with tomatoes and their juice.

Step 3

Heat a large saucepan over medium heat. Add onion and garlic and cook, stirring frequently, until beginning to brown, 4 to 6 minutes, adding water by the tablespoon if it starts to stick. Pour it all into the blender along with the chipotle powder and process until smooth.

Step 4

Return the pot to medium heat. When hot, add the puree and stir nearly constantly until thickened to the consistency of tomato paste, about 6 minutes. (Careful–watch for hot, bubbling “eruptions”!) Add broth, water, oregano (if using), and drained pinto beans. Bring to a boil, then adjust heat to maintain a simmer. Simmer for 30 minutes.

Step 5

While the soup is cooking, prepare the tortillas. Preheat oven to 375F. Cut each tortilla in half (can be done in a stack if you have a sharp knife). Then cut each half into 1/4-inch wide strips. Place the strips in a single layer on a baking sheet and sprinkle with salt, if desired. Bake for about 15 minutes, stirring every 5 minutes, until golden brown. Remove from oven and allow to cool uncovered until soup is ready.

Step 6

Add spinach (or chard 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 for spinach, longer for chard or kale.

Step 7

Ladle the soup into 6 soup bowls. Divide avocado and tortilla chips among the bowls. Serve warm, with lime wedges.