Sort and soak beans overnight; drain and discard soak water. In a 4-quart pot, saute onion in butter or marg until tender but not browned. Add soaked beans, 4 cups water, bouillon cube, ham (cut into 4-6 chunks), bay leaves, thyme, oregano, salt & red pepper. Bring to boil; reduce heat. Cover and simmer until beans are tender, 1 to 1-1/2 hour. Remove 1 c. beans from stew, mash in a bowl with potato masher or fork. Add mashed beans to stew; stir to thicken. Remove ham and dice. Remove bay leaves and red pepper, if used and discard. Add diced meat, green pepper and rum (if desired) to beans. Cover and simmer 15 minutes. Serve beans over rice and top with sour cream if desired.