Soak the beans, then drain.
Cover with 8 cups of water.
Simmer covered for about 1 1/2 hours or until the beans are almost tender.
Combine green bell pepper, onion, oregano, cumin, bay leaf, and a little cooking water in a blender.
Blend on low until the mixture is smooth.
Add blended mixture to the beans.
Bring to a boil again, then reduced heat to a simmer.
Add salt, sherry, and vinegar.
Simmer, uncovered until the bean mixture becomes thick, about 2 hours.
