For the beef stock, preheat the oven to 230C/450F/Gas 8.
Place the beef bones into a roasting tray and sprinkle over the salt flakes. Roast in the oven for 25-30 minutes, or until well browned.
Add the onions, carrots and celery to the roasting tray and return to the oven for a further 12-15 minutes, or until the vegetables have browned.
Transfer the bones and vegetables to a large stock pot.
Add the light beer to the roasting tray and bring to a simmer, scraping up any browned bits up from the bottom of the tray using a wooden spoon to deglaze. Add the mixture to the pan.
Add the bouquet garni, peppercorns, garlic cloves, tomato purée and bay leaves to the pan and stir well. Add the water and bring the mixture slowly to the boil. Reduce the heat until the mixture is simmering, then continue to simmer gently for two hours, skimming off any fat that rises to the surface of the liquid at regular intervals.
Strain the stock into a clean pan and set aside to cool (skim off any remaining fat before using).
For the Yorkshire pudding, decrease the oven temperature to 220C/425F/Gas 7.
Sift the flour with the salt into a bowl and make a well in the centre.
Gradually add the beaten eggs to the well and work it into the centre of the flour mixture a little at a time. Gradually whisk in the milk a little at a time until the batter has the consistency of single cream. Set aside for at least an hour to rest.
When the batter has rested for one hour, drizzle a little oil into each of the wells of a 12-hole Yorkshire pudding tray.
Heat the oil in the oven until smoking hot, then quickly three-quarters fill each well with some of the Yorkshire pudding batter using a ladle and return to the oven. Bake for 25-30 minutes, or until the Yorkshire puddings have risen and are golden-brown.
Meanwhile, for the gravy, place the sliced beef fat into a large frying pan over a medium to high heat and sprinkle over the salt. Fry for 2-3 minutes, or until the fat begins to melt. (Remove any strips of fat that haven't melted from the pan and discard).
Add the onions to the hot fat and fry for 4-5 minutes, or until softened. Add the beef stock and beer and bring the mixture to the boil. Reduce the heat until the mixture is simmering, then continue to simmer for 15 minutes, or for longer if you prefer thicker gravy.
Add the redcurrant jelly and stir well until dissolved. Continue to simmer for a further 4-5 minutes. Season, to taste, with salt and freshly ground black pepper. (NB: The leftover beef stock can be set aside to cool, then frozen in ice cube trays and kept for up to six months.)
To serve, place two Yorkshire puddings onto the centre of each of four serving plates. Arrange three of the black pudding sausages between the Yorkshire puddings. Drizzle over the gravy.