Start by finely chopping your onion, carrot, and celery while your heavy bottom pot preheats over medium-low. Once the pot is hot, add your butter and olive oil. Let the butter melt before adding in the onions.
Gently fry the onions for 2 minutes before adding the carrot and celery. Stir occasionally and gently cook for another 4-5 minutes until softened but not browning.
Now add the ground meat and salt. Break it up with your spatula and turn the heat up to medium to cook the meat almost all the way through, stirring occasionally.
Once there is very little pink left in the meat, add the wine or broth/stock and turn the heat up to medium high until it begins to simmer. Reduce the heat to medium low and let it gently boil for 20 minutes until completely reduced and you can hear the oil sizzling.
After the sauce has reduced, add the milk and the fresh nutmeg. Let the milk come to a gentle simmer, then reduce the heat to low and let the sauce reduce for another 15 minutes. Try not to let it boil to vigorously or the milk will separate.
Now add the tomato puree and the tomato paste. Stir well, then bring the sauce to a gentle simmer. Partially cover the pot with a lid and put it on a low heat burner (if you’re using gas) and let it reduce slowly over the next 3 hours. Stir occasionally.
After 3 hours, taste and adjust salt. Use in lasagna, serve immediately with pasta, or freeze in small containers for quick weeknight dinners.