Sort and soak beans overnight; drain and discard soak water. In a 4 litre pot, saute onion in butter until tender but not browned. Add soaked beans, 4 cups water, bouillon cube, ham (cut into chunks), bay leaves, thyme, oregano, salt and pepper. Bring to a boil, reduce heat. Cover and simmer until beans are tender, 1 to 1- half hours. Remove 1 cup of beans from pot and mash with a potato masher or fork. Add mashed beans back into pot and stir to thicken. Remove ham chunks and dice. Remove bay leaves and red pepper, if used and discard. Add diced ham, green pepper and rum to beans. Cover and simmer for 15 minutes. Serve beans over rice and top with sour cream if desired.