In a heavy saucepan or casserole, melt the butter and the oil of medium heat. Add the oxtail pieces and cook, turning frequently, until golden brown on all sides. Transfer to a plate and reserve.
Add the onion, carrot and celery to the pan. Cook until soft and lightly browned, 8-10 mins. Add the flour and stir until it browns, 3-4 mins.
Remove pan from the heat and allow to cool for 2-3 mins. Stirring continuously with a whisk, slowly add the stock. Return to the heat and continue to stir until the soup comes to a boil and starts to thicken.
Return oxtail pieces to pan along with the bouquet garni. We have used 3/4 tsp dried parsley, 1/2 tsp dried thyme and 1/2 tsp crushed black pepper instead of the bouquet garni.
After the soup comes to a boil again lower heat and skim surface fat. Simmer the soup partially covered for 3-3-1/2 hours, skimming surface fat from time to time. Remove from the heat.

Extract the oxtail pieces. Remove meat and discard bones. Remove bouquet garni. Strain the soup through a sieve into a bowl. *See notes*

Finishing the soup
Reheat soup to a simmer. Add diced carrot and turnip plus the reseerved meat and simmer for 15 mins, or until the vegetables are barely tender. Just before serving, add salt and pepper to taste and stir in the port wine.
Serve with a full flavoured beer.