Because it's made with just a handful of basic ingredients, this soup is easy and inexpensive to prepare (you'll need to set aside a few hours for soaking and simmering the beans, though). The mild flavor of the soup is pleasing on its own, but traditional add-ins like rice, egg, and onion make it even more appealing and hearty.
In a large pot, bring the beans and water to a full boil. Remove the pot from the heat, cover it, and let stand for 1 hour.
Return the pot to the stove and bring the mixture to a boil. Add 1/2 cup cold water to stop the rapid boil, then reduce the heat to medium-low. Stir in the chicken broth and black pepper, cover, and simmer for 1 hour.
While the beans cook, heat the oil in a skillet over medium heat. Add the onions, green peppers, and celery, and saute them until they are soft, about 10 minutes. Add the garlic, cumin, bay leaf, salt, and sugar, and cook for 1 more minute.
Stir the mixture, along with the vinegar, into the beans, cover the pot, and continue cooking for 1 more hour or until the beans are soft. More water can be added if the soup becomes too thick.
Remove the soup from the heat and allow it to cool for 30 minutes. Discard the bay leaf and puree the soup, two cups at a time, in a blender or food processor. Tip: You can skip the cooling period if you use a hand blender for this step.
Return the soup to the pot to reheat it. Add salt and pepper to taste. Serve the soup with side bowls of chopped eggs, minced onions, sour cream, rice, and cilantro for add-ins. Makes about 14 cups.
Per serving (1 cup): Calories 154 • Total Fat 3 g • Saturated Fat 0.3 g • Cholesterol 1 mg • Sodium 700 mg