Step 1

Heat the oven to 325°F with the rack in the lower-middle position. In a large Dutch oven over medium, heat the oil until shimmering. Add the pancetta and cook, stirring occasionally, until lightly browned, about 3 minutes.Add the carrots and celery, then cook, stirring occasionally, until the vegetables begin to soften, 3 to 5 minutes. Add the wine and cook, scraping up any browned bits, until reduced by about half, about 3 minutes. Add the onions, beef, pepper flakes, Parmesan rind (if using), 1/4 teaspoon salt and 1 teaspoon black pepper, then stir to combine. Cover, transfer to the oven and cook for 1½ hours.

Step 2

Remove the pot from the oven and stir. Return to the oven, uncovered, and cook until stewy and the meat falls apart when pressed with a fork, about another 1½ hours. Tilt the pot to pool the cooking liquid to one side, then use a wide spoon to skim off and discard as much fat as possible. Remove and discard the Parmesan rind (if used). Cover and set aside while you cook the pasta.

Step 3

In a large pot, bring 4 quarts water to a boil. Stir in the pasta and 1 tablespoon salt, then cook, stirring occasionally, until al dente. Reserve about 1 cup of the cooking water, then drain the pasta.

Step 4

Add the pasta to the Dutch oven and toss to combine with the sauce, adding about ½ cup of reserved pasta water. Add the parsley and half the grated Parmesan, then toss again; add more reserved water as needed so the sauce coats the pasta. Taste and season with salt and black pepper. Serve with the remaining Parmesan.