Sort and wash beans. Place in a large Dutch oven, and cover with water 2 inches above beans; let soak overnight. Drain beans, and return to Dutch oven; add water and onion. Bring to a boil. Reduce heat; cover, and simmer 2 to 3 hours or until tender, adding more water if necessary.
Process beans in electric blender until smooth. Return mixture to Dutch oven; stir in remaining ingredients. Cook over low heat, stirring frequently, until thoroughly heated.