Preheat your oven to 200°C/Gas Mark 6

Rub half of the bacon fat over the oxtail and place it on a roasting tray, and put it in the oven for 20-25 minutes until it's browned all over the outside. If you want to be super thorough, turn it over and give it another 10 minutes for the bottom to brown too. 

Once it's done, remove it and put to one side. Turn the oven down to 165°C/Gas Mark 3.

While the oxtail is busy in the oven, heat the rest of the fat in a heavy bottomed casserole pan and add the garlic and the vegetables and thyme. Cook until they just start to brown. Add the red wine and scrub any stick bits off the bottom of the pan. 

Take off the heat, add the oxtail, and the stock - it should just cover the contents. 

Pop on a lid and put the whole dish into the oven and leave for at least 5 hours. 

Half way through the cooking time, remove the lid. This will let the liquid evaporate a little bit. You can do this on the hob, or ignore this if you're wanting to turn it into stew.

Whilst the oxtail cooks, you've plenty of time to make the pastry and get it chilled.

Once the cooking time is up, let it cool and remove the bones. 

Sieve the flour into a bowl. 

Add the butter and either use a processor to pulse the butter into the flour until it resembles breadcrumbs, or use your fingers to rub it into the flour, again until it resembles fine breadcrumbs.

Add the milk, a tablespoon full at a time until it comes together. You want to add as little as possible -  too much liquid will make a tough pastry.

When it all comes together, roll it into a ball, wrap it in waxed paper or clingfilm and let it sit in the fridge until you need it (it needs a minimum of 30 minutes chill time in the fridge). 

Now we have both parts to our pie ready to pull together. 

Roll out your pastry. This should be enough to fill a 23cm tin (I used a square one because corners means more pastry for dunking). 

Line the bottom of the tin and, if you prefer (like I do) blind bake the base to prevent a soggy bottom. To do this: once your base is lined with pastry prick it all over and, put it back in the fridge for 5-10 minutes and in the meantime preheat your oven to 190°C/Gas Mark 5. Remove the pastry from the fridge and brush it with the beaten egg. Pop it into the oven for about 15-20 minutes, until it browns. Check it half way through and if it's bubbling on the base, prick it again before putting it back in. 

I would at this point like to say that my pastry always shrinks, so if yours fails, you're in good company. 

Once it's baked, put the filling in. 

Then top it with more pastry, make a couple of holes for steam to escape and brush the lid with more of the beaten egg. 

Put it in the oven for 45 minutes on 190°C/Gas Mark 5, until the centre is cooked through.