Begin by heating a pot over medium heat. Add the diced pancetta and cook for about 5-8 minutes, allowing it to get slightly crisp and fat to render. Remove it from the pot. Add the onion, carrots, and celery to the pot. Sauté for 5-7 minutes until softened. Season with a pinch of salt. Add the garlic and cook for an additional minute.
Add the ground beef to the pot, breaking it up with a spoon. Cook for about 8-10 minutes until fully browned. Season with salt and pepper.
Push the meat and vegetables to the side of the pot, and add the 6 oz can of tomato paste in the center. Toast the tomato paste for 5-6 min, stirring frequently, until it turns a deep brick color and begins to caramelize. This step adds a deep, rich flavor to the sauce.
Pour in the white wine, using a wooden spoon to scrape up any browned bits from the bottom of the pot. Let the wine simmer and reduce by half, about 3-4 minutes. This deglazing step ensures you capture all the flavor from the pan.
Add the pancetta back in. Stir in milk and simmer for 5 minutes. After the milk has had time to meld with the meat, add the crushed San Marzano tomatoes, nutmeg, Thyme and bay leaf. Stir everything together and reduce the heat to low.
Cover the pot and let the sauce gently simmer for at least 1.5 hours up to 8 hours, stirring occasionally. This long, slow cooking process is key to developing the deep, rich flavor typical of Bolognese.
Right before serving, cook the pasta. Discard the bay leaf and thyme sprig. Toss the pasta, adding a splash of the reserved pasta water if needed Serve topped with freshly grated Parmesan and garnish with fresh basil or parsley if desired.
