Sopa de Frijol NegroMore than twenty years ago, I prepared this black bean soup for a class, and the majority of the twenty or so students attending had never before seen black beans. How times have changed, and now we know what the Mexicans have known for centuries—black beans are delicious!For the best flavor, cook the beans a day ahead. chiles are tiny red dried chiles that are quite fiery. Sherry imparts a lovely flavor and shows Spanish influence. -style sherry is aged, for a richer, mellower flavor.