Preheat oven to 325º. In a large, heavy-bottomed pot with a tight-fitting lid, heat the olive oil until shimmering. Sear seasoned beef on all sides (cut beef in half, if necessary).
Immediately add butter, onions and garlic and stir occasionally for 2 min. Add all remaining ingredients except mushrooms, pasta and garnishes. Cover tightly and place in pre-heated oven.
After 2 hr, add mushrooms. Cook covered at least one more hour until beef is so tender that a fork will easily push through center of roast. (The cooking time can be dramatically sped up to about 1 hr with a pressurized instant cooker; follow manufacturer directions). Transfer all beef and solids to a holding dish or bowl, reserving all juices in pot. In a separate pot, cook pasta to al dente, then toss hot pasta in reserved pot roast juices. Transfer pasta to a serving bowl, shredding beef and onions over top. Garnish generously with cheese and parsley.