Preheat the oven to 170°C.
Coat seasoned oxtail pieces in flour after washing and drying.
Brown the oxtail in oil for 10 minutes and transfer to a casserole dish.
Soften sliced onions, garlic, carrots, and celery in the frying pan for 10 minutes.
Add vegetables, herbs, wine, stock, and tomato purée to the beef and simmer.
Cover and cook in the oven for three hours until the meat is tender.
Skim fat, shred the meat from the bones, and return chunks to the casserole with sherry and yeast extract.
Mix dumpling ingredients with water to create a soft dough.
Drop 18 dough balls onto the simmering soup, cover, and cook for 15-18 minutes.