Place the oxtail joints in a large saucepan, cover with cold water and bring to the boil; strain and dry very well. In a large pan, add oil and brown the oxtail pieces one by one, to avoid lowering the temperature. Repeat with remaining oxtail pieces and drain. Add vegetables and brown lightly.
Return meat to the pan with the thyme, seasoning and stock. Bring to the boil, cover and simmer gently for three to four hours. Strain the soup and set aside the oxtail bones. Cool the soup. Remove all the meat from the oxtail bones and shred finely.
Remove the layer of fat from the surface of the soup. Add oxtail meat, adjust seasoning and stir in sherry.

Serve the soup with green peas, truffle oil and croutons.