In a large Dutch oven, heat olive oil over medium heat. Add pancetta and cook until crispy, about 5 minutes. Add onion, carrots, and celery. Sauté for 8-10 minutes until softened and lightly golden, stirring often. Add garlic and cook 30 seconds just until fragrant.

Push vegetables to the sides, increase heat to medium-high. Add beef in an even layer, season with salt and pepper. Let it sear undisturbed for 3-4 minutes until a dark crust forms. Break up and continue cooking until all pieces are deeply browned, no longer pink, and reach an internal temperature of 160°F (71°C), about 10 minutes total. Don't crowd the pan; cook in batches if needed.

Pour in the red wine, scraping up every bit of browned fond from the bottom. Bring to a boil and cook until the wine is almost completely evaporated, 3-4 minutes. The mixture should look dry again.

Clear a small spot in the pot, add the tomato paste directly onto the hot surface. Stir and cook for 2 minutes until it darkens to a brick-red and smells sweet. Then incorporate it into the meat mixture.

Add the crushed tomatoes and milk. Stir well, bring to a gentle simmer. Reduce heat to low, cover partially with a lid (leave a small gap). Simmer for at least 1 hour, stirring every 15 minutes, scraping the bottom. For maximum thickness, simmer 2-3 hours, adding beef broth only if it becomes too dry.

When the sauce is thick, glossy, and a spoon dragged through leaves a trail that slowly fills in, remove from heat. Swirl in the cold butter until emulsified. Taste and adjust salt. Serve immediately over pasta, topped with Parmesan and basil.