Heat a wide, heavy-duty 6- to 8-quart pot over medium heat. Add the pancetta and cook until its fat begins to render, 2 to 3 minutes. Add the carrot, onion, celery, and garlic and cook until the vegetables begin to brown, 4 to 6 minutes. Stir in the fennel seed and pepper flakes.
Add the tomatoes and white wine. Boil for 2 to 3 minutes, then add the broth, milk, parsley, and bay leaves. Stir well, return to a boil, and season with a little salt. (Underseason, as the sauce will reduce and concentrate the salt.) Lower the heat to medium low and simmer until reduced by about one-third, 30 to 40 minutes.
Add the turkey, raise the heat to medium, and bring to a boil. Reduce the heat to medium low and simmer until the flavors are fully developed and the sauce is thick and rich, 10 to 15 minutes. Discard the bay leaves and season to taste with salt.
Cook the pasta in boiling salted water according to package directions; drain. Toss the pasta with the bolognese and serve.