Heat the oil in a large saucepan; when hot, saute the onions until golden brown, about 5 minutes. Add crushed tomatoes to the saucepan.
Stir in the oregano, basil, salt and pepper and simmer 1 hour to concentrate flavors.
While the sauce is cooking, heat 4 T of the butter in a skillet over medium heat. Saute the mushrooms and hot pepper flakes until the mushrooms are golden.
Carefully add the vodka and simmer for 5 minutes to cook off the alcohol.
Add the heavy cream and bring to a simmer; pour the cream mixture into the tomato puree; stir to mix. Keep the sauce warm while cooking the pasta.
Add the kosher salt to 6 quarts of water. Bring to a rolling boil. Add pasta to boiling water; cook uncovered until pasta is al dente, about 12 minutes. Drain well.
Melt the remaining 4 T of butter in a large skillet. Stir in pasta to glaze, then add Parmesan cheese and mix thoroughly. Stir in 1/3 or the sauce and mix with the pasta; divide among plates. Top each plate with some additional sauce; pass remaining sauce and additional cheese at the table.