Chicken Tortilla Soup

medium dried pasilla (negro) chiles, stemmed and seeded**

diced fire-roasted tomatoes in juice

olive oil

medium white onion, sliced 1/4-inch thick

garlic cloves, peeled

good-quality chicken broth

large epazote sprig (optional)

(about 1 1/4 pounds total) boneless, skinless chicken breast halves, cut into 1/2-inch cubes

large ripe avocado, pitted, flesh scooped from the skin and cut into 1/4-inch cubes

shredded Mexican melting cheese (like Chihuahua, quesadilla or asadero) or Monterrey Jack

roughly-broken tortilla chips

Mexican crema, sour cream or creme fraîche for garnish

large lime, cut into 6 wedges, for serving

fresh chopped cilantro, for serving

cotija cheese, for serving (optional)