Before you start, get the mince up to room temperature.
In heavy-bottomed saucepan or Dutch oven, add the pancetta and cook until crispy. Remove from the pan and set aside.
Add the olive oil and butter to the fat over medium heat. Add the onion, celery and carrot and sweat down until the vegetables are translucent.
In the meantime, combine the two portions of mince together in a large bowl. Add a little olive oil and, using your very clean hands, combine the mince.
Add the garlic to the vegetables and stir for one minute to combine. Do not let the garlic burn or it will make the finished ragù bitter.
Add the pork and beef mix and stir into vegetables. Brown over medium-high heat, stirring to keep meat from sticking together. This should take 15 to 20 minutes, so be patient, it’s worth it.
Once the ragù is browned, add the tomato paste and work into the ragù until the paste ad really deepened in colour. Add the pancetta back into the ragù.
Add the milk and simmer while stirring until the milk is reduced, around 2-3 minutes.
Add the wine and stir until evaporated.
Add the stock, bring to a boil and then lower the heat as low as you can go.
Put the lid on the pot and simmer for 1 1/2 hours, stirring every 15 minutes.
Remove the lid slightly and simmer for another 1 1/2 hours, moving the lid every 15 minutes until fully off. If the ragù is starting to dry out add some more stock or water, just enough so that you can see liquid bubbling around the ragù.
The final ragù should have a film of oil around the pieces of mince. It should bubble around the sauce. If not, add more stock.