1 tablespoon plus
1/2 teaspoon tomato paste
3/4 cup beef broth, heated to a simmer
1/3 pound flat pancetta, finely chopped
1 carrot, finely chopped
1 celery stalk, finely chopped
3/4 cup finely chopped onion
3/4 pound ground beef (not lean)
Fine sea salt
Freshly ground black pepper
1/2 cup dry white wine
3/4 cup whole milk
3/4 pound pasta alla chitarra
Whisk tomato paste into broth; set aside.
Cook pancetta in a wide heavy pot over medium heat, stirring occasionally, until lightly golden and fat is rendered, about 5 minutes. Add carrot, celery and onion, and cook, stirring occasionally, until vegetables are tender, about 8 minutes. Add beef and cook for 10 minutes more, stirring frequently with a wooden spoon and breaking up clumps into tiny bits. Season with generous pinch salt and pepper.
Add wine and cook until evaporated, about 5 minutes, then add broth mixture, reduce heat to low and very gently simmer, covered, stirring occasionally, for 30 minutes. Add half of the milk and continue cooking, covered, for 30 minutes more. Add remaining milk, then cook, covered, stirring once or twice, for 1 hour more (total cooking time is 2 hours). Season with salt and pepper to taste.
Bring a large pot of salted water to a boil. Add pasta and cook until al dente. Drain and immediately toss with ragù.