Finely chop the celery, carrot, garlic, and onion. Pulse the onion and garlic in a small food processor and the celery and carrot in a large blender. Mix all together in a separate bowl, to combine. Set aside.
In a large heavy-bottomed saucepan, heat the oil and butter over a low to medium heat. Be careful to not let the butter burn. Add the pancetta/bacon, just to soften. Then, add the celery, carrot, garlic, and onion mixture and stir to coat well. Sweat the vegetables in the pan, stirring every now and then, for a good 10-12 minutes. You want them to melt and break down. Then, add the ground beef, crumbling with your hands as you go. Leave it to sear and take on color. Turn it often with a spoon or spatula to make sure the meat is browned and has "caught" the bottom of the pan a little.
Season with generous salt and pepper, as well as a few sprinkles of crushed red pepper to taste. Add the wine and bring to a simmer to cook out the alcohol. Add the bay leaves, thyme, and tomatoes and stir to combine. Bring the sauce to a boil, then reduce the heat to maintain a gentle simmer and cook until it has reduced slightly, 5-10 minutes. Add the milk. Cover the pan, reduce the heat to low and simmer very gently for 1 to 1 1/2 hours. Taste and adjust the seasoning as needed.
Meanwhile, bring a large pot of salted water to a boil. Cook the pasta accordingly. Drain the pasta.
Serve the sauce over the pasta, topped with a good grating of Parmesan. Enjoy!