Black Bean Soup

1. FOR THE BEANS: Place water, beans, ham, bay leaves, and baking soda in large saucepan with tight-fitting lid. Bring to boil over medium-high heat. Using large spoon, skim foam from surface as needed. Stir in salt, reduce heat to low, cover, and simmer briskly until beans are tender, 1-1⁄4 to 1-1⁄2 hours (if after 1-1⁄2 hours the beans are not tender, add 1 cup more water and continue to simmer until tender); do not drain beans. Discard bay leaves. Remove ham steak, cut into 1⁄4-inch cubes, and set aside.
2. FOR THE SOUP: Heat oil in Dutch oven over medium-high heat until shimmering. Add onions, carrot, celery, and salt and cook, stirring occasionally, until vegetables are soft and lightly browned, 12 to 15 minutes. Reduce heat to medium-low, add garlic, pepper flakes, and cumin and cook, stirring constantly, until fragrant, about 3 minutes. Stir in beans, bean cooking liquid, and chicken broth. Increase heat to medium-high and bring to boil, then reduce heat to low and simmer, uncovered, stirring occasionally, to blend flavors, about 30 minutes.
3. Ladle 1-1⁄2 cups beans and 2 cups liquid into food processor or blender, process until smooth, and return to pot. Stir together cornstarch and water in small bowl until combined, then gradually stir half of cornstarch mixture into soup. Bring to boil over medium-high heat, stirring occasionally, to fully thicken. If soup is still thinner than desired once boiling, stir remaining cornstarch mixture to recombine and gradually stir mixture into soup; return to boil to fully thicken. Off heat, stir in lime juice and reserved ham; ladle soup into bowls and serve immediately, passing garnishes separately. (Soup can be refrigerated for up to 4 days. If necessary, thin it with additional chicken broth when reheating.)

BLACK BEAN SOUP WITH CHIPOTLE CHILES
The addition of chipotle chiles in adobo—smoked jalapeños packed in a seasoned tomato-vinegar sauce—makes this a spicier, smokier variation on Black Bean Soup.
Omit pepper flakes and add 1 tablespoon minced canned chipotle chile in adobo sauce plus 2 teaspoons adobo sauce along with chicken broth in step 2.