For the roast potatoes: cut the top and bottom off each potato and peel the remainder, shaping the potato into a barrel. You should have 3 barrels per person.
Put the potatoes into a large saucepan of boiling salted water, and cook for about 10-15 minutes, until they are half-done. Drain and cool.
For the beef: take the backbone off the beef. Remove the big nerve and the fat. Bash out the back fat and trim it, then tie it and the backbone back onto the meat. Alternatively, ask your butcher to do this for you.
Preheat the oven to 220C/200C fan/Gas 7. Weigh the beef and calculate the cooking time, allowing 15 minutes per 450g, which will give rare meat. For medium-rare add 15 minutes to the total cooking time, for well done add 30 minutes.
Put the beef in a roasting tin. Smear it with 55g of the dripping and season well with sea salt and freshly ground black pepper. Roast for 30 minutes, then turn the oven temperature down to 180C/160C fan/Gas 4 and finish cooking for the time calculated. Remove the joint from the oven and the roasting tin and leave it to rest for 20 minutes. Keep the roasting tin and the residual fat in it for later on.
For the yorkshire puddings: put the flour in a large bowl. Add the eggs and the combined milk and water and whisk until smooth. Stir in a pinch of sea salt and the vinegar and leave for to rest for 30 minutes.
Preheat the oven to 240C/220C fan/Gas 9. Heat the lard in some muffin tins (straight-sided work best) in the oven until the fat is smoking. Beat any lumps out of the batter then pour it quickly into the tins and put them back into oven. Bake for 15 minutes, then reduce the oven temperature to 180C/160C fan/Gas 4 and continue cooking until they are golden and risen.
Meanwhile, put the potato dripping (3-4 tbsp) into a roasting pan and heat in the oven for 5 or so minutes. Then tip the par-boiled potatoes into the pan with the dripping and roast at 200C/180C fan/Gas 6 for about 40 minutes or until they are crisp and cooked. Season with sea salt and freshly ground black pepper.
For the gravy: fry the sliced onion in the roasting tin used to cook the beef with the extra 1-2 tablespoons of dripping. When lightly coloured, pour off the excess fat. Add the white wine and boil until the volume of liquid has reduced by half. Next add the stock, bring to the boil and reduce by a third. Whisk in most of the cold butter, mixing well. Taste and adjust the seasoning then strain the gravy into a clean saucepan.
. In a separate pan, fry the spring onions in the remaining butter for 5 minutes, then pour the contents of the pan over the gravy. Bring to a simmer, adding the juices from the rested meat. Just before serving, add the parsley.
. When the beef has rested, take the bone and fat off the joint. Cut away the rib bones and carve the meat. Serve on a large platter, handing the gravy, Yorkshire puddings and potatoes separately.