In a medium saucepan over medium-high heat, cook the bacon until it is crisp and has released almost all of its fat, about 6 minutes. This is called rendering.
Add the onion, carrots, celery, salt, and pepper and cook, stirring frequently, until the vegetables are very soft and lightly browned around the edges, about 6 minutes.
Add the ground chuck and cook, stirring to break up any clumps, until the meat is browned, about 5 minutes.
Add the vinegar, garlic, and tomato paste and cook for 2 minutes, stirring constantly.
Add the beef broth and bring to a boil. Lower the heat so that the sauce just simmers. Simmer, partially covered, for 15 minutes.
Combine the milk and cream in a small mixing bowl. After the sauce has simmered for 15 minutes, and at even intervals, start adding the milk-cream mixture little by littleó1/4 cup or so at a time over 11/2 hours. By the end of the 11/2 hours, the milk mixture should be completely incorporated and the sauce should be very thick and creamy. This sauce is not supposed to be very ìsaucyîóit should be tender morsels of meat coated by a thick, creamy sauce.
Transfer the cooked pasta to a large heatproof bowl and add the sauce. Toss the pasta with the sauce and serve immediately, garnished with grated Parmesan cheese, if desired.
Yield: 4 - 6 servings