In stock pot or large kettle, heat olive oil and sauté garlic, onions, and celery until tender. Add chicken broth, left over ham and ham bone, and bay leaf; simmer for 1 hour. Add the black beans, red bell pepper, cumin, cayenne pepper, salt, black pepper, brown sugar, lemon juice, and sherry.
Simmer for 20 to 30 minutes. Puree about 1/4 to 1/3 of the soup then mix it back into the pot. If desired, remove ham bone and cut off as much meat as possible and add to soup. Add chopped parsley. Top each serving with a dollop of sour cream and sprinkling of chopped green onions.