An Italian ragù sauce is about flavouring the meat, so isn't a tomato sauce as such - the big thing here is the beef. The unauthentic element is the Guinness, which is almost anti-Italian but the malt really works. Still, it's best cooked a day before serving, as the flavours will become more intense if left in the fridge overnight. A large cast-iron pot for this is perfect, as it retains the heat, but any large pot will do.
Heat some olive oil in the pot and brown the beef lightly on each side. If you can't do it all at once, do it in batches. Return all the beef to the pot. Add the onion, the shallots, the garlic, the mushrooms, all the tomatoes, the chilli and then pour in the Guinness. If it doesn't cover everything add a little water. Bring close to the boil, and there's likely to be a fair bit of foam from the Guinness. Turn the heat down until everything is simmering and then add the red wine, the tomato puree and the beef stock. Add a large pinch or grind of sea salt and black pepper. Give the sauce a good stur, lower the heat a little until the sauce is gently bubbling then leave for an hour or so.
After an hour give it a good stur, and you should have a thin but rich sauce with beef, onions, mushrooms and tomato. If it's dry, add some water. If it's too thin, turn up the heat a shade. Either way, your kitchen will smell wonderful. Gently heat until the sauce is rich and glossy and the beef is tender, which will probably take another hour. Stir in the basil and thyme. Allow to cool and reheat when required.
Cook the tagliatelle as per the packet instructions. Serve with the ragu on the tagliatelle and plenty of parmesan on top.