Sopa Tarasca

Drain and rinse beans.

Heat oil in a large pot over medium-high heat. Add onions and cook, stirring occasionally, until tender, 3 to 5 minutes. Add garlic, cumin and chili powder; cook, stirring, for 30 seconds. Add the drained beans and water. Bring to a boil over high heat. Reduce heat to maintain a simmer, cover and cook until the beans are tender, 1 to 1 1/2 hours.

Meanwhile, soak chiles in boiling water until the skins have softened, about 15 minutes. Drain and chop.

Add the chiles, tomatoes and their juice, salt and pepper to the beans. Puree the soup in a regular blender (in batches, if necessary) until very smooth. (Use caution when blending hot liquids.) Serve topped with avocado and garnished with queso fresco, limes and tortilla chips, if desired.