Heat a large heavy-based saucepan.
When it is hot, add a little sunflower oil and brown the meat in batches over a high heat.
Use a little more oil in necessary, to keep meat from burning and sticking to the saucepan.
Reduce the heat and heat the remaining sunflower oil.
Sauté the onions until golden.
Add the flour and stir until the mixture starts to brown.
Stir in the beef stock
and then return the meat to the pan and add the bay leaves,thyme,garlic, sugar, red wine, tomato paste and half each of the carrots and celery.
Bring to the boil then reduce the heat and cook for another hour until the meat is very tender.
Add the parsley and lemon zest.
Season to taste with salt and freshly ground black pepper.
Remove the oxtail pieces from the soup with a slotted spoon.
Pull the meat off the bones, then return it to the soup and discard the bones.Serve with melba toast.