Add the pancetta to a large pot over medium heat and cook for 4–5 minutes, until the fat has rendered and the pancetta is golden. Add the olive oil, onion, carrot, celery, and a pinch of salt. Sauté for 6–7 minutes, stirring regularly, until the soffritto has softened and become aromatic.
Increase the heat to medium-high. Add the beef, veal, and pork mince and cook for 8–10 minutes, or until no longer pink and any released water has evaporated. Season with salt and pepper.
Add the red wine and tomato paste, if using, and bring to a simmer. Let the wine reduce by 75%. Add the tomato passata and the water used to rinse the jar. Mix well and season to taste.
Bring the sauce to a light boil, mix well, then reduce the heat to medium-low and simmer for a minimum of 2 hours, up to 5 hours for a deeper flavour.
Meanwhile, prepare the pasta: bring a pot of water to a boil and season generously with salt. Cook the pasta 1 minute less than the packet instructions. Reserve some pasta water.
Once the ragù has cooked for at least 2 hours, add the milk and mix gently so it doesn't split. Check the seasoning and remove from the heat.
In a pan or bowl, combine a ladle or two of ragù with the cooked pasta, a small handful of Parmigiano Reggiano, and freshly torn basil. Mix well to coat the pasta, adjusting the consistency with reserved pasta water if needed. Serve in bowls, garnished with more Parmigiano Reggiano and basil. Dig in.