To make the original meat sauce for lasagne alla bolognese, start by finely chopping the celery, unpeeled fresh carrot (if using) and onion with a knife. Heat the oil in a pan and add the chopped vegetables. Cook for about ten minutes over low heat, stirring occasionally.
After about 10 minutes, the vegetables will be wilted and the bottom of the pan should be dry. At this point, we can add the coarse ground beef and pork (fresh fatty pancetta will also work). The meat should also brown slowly for about ten minutes, so stir well until the meat appears browned. At first, the juices will come out, but once they dry out, you can add the 250 g of white wine (or red, depending on preference).
When all the wine has evaporated, pour the tomato passata into the pan and add 1 liter of water and a pinch of salt. Let the meat sauce simmer over medium-low heat for one hour, keeping an eye on it. After the first hour, add the second liter of water, stir and continue cooking for another hour.
After the second hour of cooking, pour the last liter of water and continue to cook over medium-low heat for another hour. This means that the meat sauce alla bolognese cooks for 3 hours with 3 liters of water added at the indicated times. At the end of cooking, the original meat sauce alla bolognese should be thick, not too dry or too liquid. Adjust the salt and pepper, turn off the heat and add the milk. Mix and set the meat sauce aside.