Preheat the oven to 300 degrees F.
Sprinkle the meat liberally with salt and pepper as much as 1 day in advance. (Cover and refrigerate it if doing so and take the meat out of the fridge 30 minutes before cooking.) Heat the oil in a large Dutch oven over high heat. When the oil is on the verge of smoking, sear the meat for about 2 minutes per side. Move the meat to the side (or remove it from the pot altogether if necessary), and add the carrots, celery root and onions. Brown the vegetables for about 3 minutes, and then add the garlic and cook for 1 to 2 minutes longer.
Pour in the wine and deglaze the pot, scraping up the browned bits on the bottom. Add the Yia Yia's Sunday Sauce, 1 cup water and the bay leaves (and the pot roast if you removed it). Bring the liquid to a simmer and taste for seasoning. Add more salt if necessary. Cover the pot and place it in the oven for 3 hours, basting the meat occasionally during cooking time.
When almost ready to serve, make the rigatoni, if using. Boil in salted water according to package directions until al dente.
Discard the bay leaves before serving. Transfer the meat to a cutting board and slice into bite-size pieces, or shred with 2 forks. Return the meat to the pot of sauce along with the drained rigatoni. Toss to coat, and serve.
Heat the oil in a 4-quart saucepan or large Dutch oven over medium heat. Add the onions and cook until translucent, 2 minutes. Add the salt and garlic and cook until everything is soft but not browned, about 3 minutes.
Squeeze the tomatoes one by one into the pan, pulverizing them by hand, and pour in their juice, too. Add the bones, wine, oregano, red pepper flakes, if using, black pepper and bay leaf. Bring the sauce to a simmer, and then reduce the heat to its lowest possible setting, and continue to cook for 8 hours. The sauce should reduce by about one-third.
Taste for seasoning and add more salt if necessary. Remove the bones and bay leaf. If not using right away, let the sauce cool, then cover and refrigerate for up to 1 week or freeze for up to 2 months. Yield: 8 cups.