Find a pan that is large enough for all the ingredients and which will fit inside your oven.
Cook the oxtail in oil over a medium heat until it is nicely brown all over. Add the wine, onion, garlic, pepper and bay leaves and bring to the boil. Put the lid on and place the pan in the oven at 185 Fahrenheit (85 Celsius) for 16 hours.
Pick the meat off the tails and throw away the tendons and bones. Put the meat back in the pan with the stock and allow it to cook until it thickens. Add salt and blackcurrant sauce to taste and stir in the butter to finish. Serve with entrecôte (see related recipe).