Place oxtails and butter in Dutch oven or large soup pot. Add carrots, turnips, onions, leek, celery, herbs, bay leaf, peppercorns, cloves, ham and 1 cup water. Cook over high heat, stirring occasionally, until vegetables soften, 8 to 10 minutes.
2
Add remaining water, except for 1/2 cup, and bring to boil. Add salt.Skim fat and scum. Simmer gently until oxtails are tender, 3 to 3 hours 30 minutes. Remove oxtails and set aside.
3
Skim fat and scum again. Strain soup, discarding vegetables, herbs, spices and ham, and return soup to pot. Combine flour and 1/2 cup water and add to soup to thicken. Add ketchup and Port. Return oxtails to soup and simmer 5 minutes.