Slow-Braised Lamb Ragu with Rigatoni and Whipped Ricotta

1 (2-lb.) boneless lamb shoulder roast, halved (see Note)

21⁄2 tsp. kosher salt, or to taste

1 T. extra-virgin olive oil, plus more for finishing

1 large yellow onion, finely diced

1 (6-ounce) can tomato paste

1 C. dry red wine

1 (28-ounce) can whole peeled tomatoes

1⁄2 C. water

1⁄4 C. plus 2 T. fresh oregano leaves

6 cloves garlic, minced

1 tsp. red pepper flakes

11⁄2 lb. dried rigatoni

1 T. minced rosemary

1 T. red wine vinegar

 

1  C. whole-milk ricotta

1⁄2 C. whole milk

1⁄2 C. packed freshly grated Pecorino Romano cheese

1⁄2 tsp. freshly ground black pepper

1⁄2 tsp. kosher salt

 

Season the lamb on all sides with 1 tsp. of the salt. Warm a large Dutch oven over medium-high heat. Add the oil, and when you just begin to see wisps of smoke, add the lamb. Sear on all sides until a deep brown crust forms, 7 to 10 minutes. Transfer the lamb to a plate and set aside. Add the onion to the pot  and  cook until just softened and lightly browned, adjusting the heat as needed, about 4 minutes. Add the tomato paste and cook, stirring almost constantly, until it darkens slightly and a deep brown crust forms on the bottom of the pot, about 2 minutes.  Pour in the wine and scrape up the bits from the bottom of the pot. Stir in the tomatoes, water, 1⁄4 C. of the oregano, the garlic, red pepper flakes, and remaining 1⁄2 tsp. salt. Nestle the seared lamb back into the pot and bring to a rapid simmer. Decrease the heat to maintain a gentle simmer, cover, and braise until the lamb is tender and easily shreds apart, about 2 hours. Remove the lamb from the sauce and shred it into bite-size pieces using two forks. Return the shredded lamb to the sauce. (It will be quite thick now but will be thinned with pasta water later.) Taste and adjust the seasoning. (At this point the ragù can be cooled to room temperature, then covered and refrigerated for up to 3 days before serving.) Return the ragù to a gentle simmer and keep it warm over low heat. Cook the rigatoni in boiling salted water until al dente according to the package directions. Drain, reserving 2 C. of the cooking water, and return the rigatoni to its pot. Stir some of the cooking water into the ragù to loosen it and add the remaining 2 T. oregano, the rosemary, and vinegar. Add a few ladlefuls of the ragù to the pot of rigatoni to lightly coat. Place the rigatoni pot over medium-low heat and cook, stirring often, to allow the pasta to absorb some of the sauce, about 2 minutes. To make the whipped ricotta: In a medium bowl, whisk the ricotta with the milk, cheese, pepper, and salt until it is loose and creamy, about 30 seconds. Use immediately or cover and refrigerate for up to 3 days. Serve the rigatoni in warm bowls, with a ladleful of the ragù spooned over each portion. Top with the whipped ricotta and a drizzle of oil.