Black bean and chipotle soup

1 tablespoon olive oil
2 medium red onions, chopped
1 medium red pepper, chopped
1 medium green pepper, chopped
4 garlic cloves, minced
4 teaspoons cumin
2 cups dried black beans
1 small can chipotle peppers in adobo
7 cups hot water
2 tablespoons fresh lime juice
2 teaspoons salt
1/4 teaspoon black pepper

1 cup plain yogurt
1/2 cup chopped seeded tomatoes
1/4 cup chopped fresh cilantro

Cook onions, red and green peppers in olive oil until soft. Add garlic and cumin; stir 1 minute. Add beans and chipotles, then 7 cups hot water. Cover and cook on high until beans are very tender, about 6 hours. Transfer 2 cups bean mixture to blender; puree until smooth. Return puree to remaining soup. Stir in lime juice, salt, and pepper. Heat through. Top with yogurt, tomatoes and cilantro.

Served with warm cornbread.