While the pasta is cooking, puree all of the blue cheese sauce ingredients in a high-powered blender until smooth.In a large pan, saute the onions and Brussels sprouts in a little water or white wine until the onions are translucent and the sprouts are tender, about 10 minutes. Add the pasta and the parsley to the pan, pour in the blue cheese sauce and cook until heated through, stirring to coat everything with the sauce.Divide among 6 plates and sprinkle with additional parsley. Serve immediately. If desired, some chopped apples may be added when you are sautéing the sprouts.