Step 1Season the pork all over with 1 teaspoon salt and pepper to taste.
Step 2In a food processor, chop together parsley, onions, garlic, pancetta and prosciutto to make a very coarse paste.
Step 3Heat the olive oil in a casserole over medium-low heat. Add the seasoning paste and another teaspoon of salt and cook until the paste is fragrant and no more liquid appears when it is stirred, about 7 minutes.
Step 4Add the pork roast, cover and reduce the heat to low. Cook, turning every 15 minutes, until the meat is lightly browned and the onions have begun to color, about 1 hour.
Step 5Add the red wine, loosely cover and continue cooking until the wine reduces to a thick sauce, about 1 hour, stirring occasionally. If, after 1 hour and 15 minutes, the wine has not reduced sufficiently, remove the roast to a plate, increase the heat to medium-high, and cook the sauce until it thickens.
Step 6Over low heat, stir in the tomato paste, 2 or 3 tablespoons at a time, stirring in each addition until it mixes into the sauce and darkens to a brick color. Stir in the crushed tomatoes, return the roast to the pan if previously removed, and cover and continue to cook, turning the meat every 30 minutes and stirring the sauce until the meat is tender enough to be easily pierced with a meat fork, 2 to 2 1/2 hours. If the sauce dries out too much and the meat begins to stick to the bottom of the pan, stir in a tablespoon or two of water.
Step 7Remove the roast to a plate and keep warm until ready to serve. Crumble the Italian sausage into the sauce and cook until the sauce is extremely dark, unctuous, shiny and thick, stirring occasionally, about another hour. (The dish can be prepared to this point and refrigerated overnight.)
Step 8Cook the pasta in plenty of rapidly boiling, heavily salted water. Warm the sauce if it has been refrigerated.
Step 9When the pasta is cooked but still slightly chewy, drain it and toss it in a bowl with the butter. Spoon over half of the sauce and toss just to coat lightly. Transfer to a serving bowl and spoon more sauce over top. Sprinkle over the Parmigiano-Reggiano and pass more on the side.