Heat the butter in a large saucepan on a low heat.
Tip in the pancetta and cook for 5 minutes until the fat is starting to melt, then scoop it out with a slotted spoon and put it to one side. Add the finely chopped onion, carrot and celery to the pan. Cook very gently for 15 minutes, stirring often, to soften and sweeten the vegetables without them browning.
Once the vegetables are soft, add the pancetta back to the pan and crumble in the minced beef, then add the salt and pepper.
Turn up the heat to medium and carry on cooking, stirring the beef around so it all cooks. Don’t worry if it starts to stick and go brown on the bottom of the pan - this will create extra flavour!
After 5 minutes, when the beef is cooked and any liquid has evaporated, tip in the white wine and use a wooden spatula to scrape up any sticky crust from the bottom of the pan, then cook for another few minutes until the wine evaporates.
Preheat the oven to 140 C. Add the tinned tomatoes and water to the pan. Mix them through and bring the sauce to a simmer, then put the lid on and put into the oven for 3 hours.
Check the pot occasionally, giving it a stir and adding another 100ml of water if it starts to look dry - although it shouldn’t.
After 3 hours, bring the pot out of the oven, remove the lid and add the milk. Cook on a low heat, uncovered, for 30 minutes. Stir it occasionally so it doesn’t stick to the bottom of the pan and let most of the liquid evaporate so you’re left with a thick, meaty ragu. Meanwhile, bring 3 litres of water to a boil in your biggest saucepan with ½ teaspoon salt.
When the ragu is almost ready, drop the dried tagliatelle into the boiling water and cook for 7 minutes, until the pasta is ‘al dente’. Drain the pasta - reserving a few ladles of the pasta water - and tip it straight into the ragu. Gently stir it all together, adding a small ladle (100ml or so) of pasta water so it stays juicy while cooking for another minute or two. The ragu should be thick and cling to the pasta, which will still have a pleasant amount of bite.
Pile the steaming Ragu Bolognese into shallow serving dishes and top with freshly grated Parmesan.