Special equipment: Cheesecloth, butcher’s twine
1. Preheat oven to 300°. Season the oxtail with salt and pepper. In a Dutch oven or large heavy-bottom ovenproof pot with lid, heat the oil over medium-high heat until it shimmers. Add the neck bones and oxtail, working in batches if necessary to avoid overcrowding the pan, and brown on all sides in the oil. Using tongs, remove the browned pieces and set them aside on a sheet pan or platter, which will collect their juices while the remaining pieces cook. Brown the sausages and set aside.
2. Once the sausages and bones have all been browned and removed from the Dutch oven, add the onion and cook over medium-high heat, stirring often and scraping the bottom of the pan with a wooden spoon so that the onion picks up the browned bits. Salt the onions a bit to release their juices as they cook.
3. Add the garlic, cook for 1 minute, then add the tomato paste, oregano and pepper flakes and cook for a few minutes, until the tomato paste is dark reddish brown and has begun to stick to the pan. Deglaze the Dutch oven with the wine and let reduce by half.
4. Add the stock, tomatoes and bay leaves. Wrap the herb sprigs in the cheesecloth and secure the bundle tightly with the twine to make a bouquet garni. Return the oxtail and bones to the Dutch oven. Season with salt and pepper and bring to a boil. Cover the Dutch oven and transfer to the oven to cook for about 2½ hours. Remove the Dutch oven from the oven, add the browned sausages and return to the oven to cook for another 30 minutes. The ragout should be thick but still juicy. Remove and discard the bouquet garni and keep the gravy and sausages warm.
5. In a large, heavy-bottom pot, bring salted water to a boil. Cook the rigatoni according to the package instructions until just al dente. Drain the pasta in a colander and return it to the hot, empty pot. Toss the rigatoni gently over medium heat for about 30 seconds to dry it completely, using tongs if necessary to keep it from sticking to the sides of the pot. Ladle in as much of the warm sauce as necessary to coat but not drown the pasta. Serve the pasta and sausages together, with the extra sauce and grated Parmigiano-Reggiano alongside.