Method

To prepare the ragù:
Heat the oil in a large casserole pot. When hot, add the finely diced onion.
Stir, season with salt, cover with a lid and turn down the heat to low.
Allow to sweat, stirring regularly, until the onion has become translucent and is completely tender. This process will take about 10 minutes.
Add the finely diced carrot and celery to the pot, stir to mix and continue cooking for a further 5 minutes to soften the vegetables.
Increase the heat and mix in the bacon lardons.
Sauté over a medium heat until the fat renders out and the bacon becomes lightly coloured.
Increase the heat to high and add in the beef and pork mince. Brown the meat, stirring regularly until the meat loses its pink colour.
Season, stir in the tomato purée and then pour in the white wine. Boil the wine until it has reduced almost to a glaze.
Add the bay leaves, rosemary sprigs and stock, bring up to the boil and then turn down the heat to the very gentlest simmer.
Allow to cook for about an hour or until reduced by at least half.
Bring the milk to a simmer and add to the meat.
Cover the sauce with a lid, leaving it slightly ajar, and continue cooking for a further 30 minutes or so at a gentle bubble, adding more stock if the ragù becomes too dry.
Remove the bay leaves, the sprigs of rosemary (or the rosemary needles if they have fallen off) and discard.
The sauce will keep in the fridge for 3 or 4 days or for a number of months in the freezer.

To prepare the pasta:
Bring a large pot of pasta water with about 4 litres of water to the boil.
Add 1½ tablespoon salt and return to the boil.
When the tagliatelle is cooked about 90% through, drain, holding back some of the pasta water.
Meanwhile, heat the ragù in a frying pan and bring to a gentle simmer.
Add the butter and swirl to combine.
Add in a good dash of pasta water and the pasta.
Simmer until the sauce coats the pasta loosely.
Towards the end, mix in a fistful of Parmesan and grate some more to bring to the table.