1Bring large pot of lightly salted water to a boil over high heat.
2Meanwhile, to make sauce, melt butter in large skillet over medium high heat. Add mushrooms, onion and garlic. Cook, stirring occasionally, til mushrooms give off their liquid, it evaporates and they begin to brown, about 7 minutes. Add wine and cook til it evaporates by half, about 1 minute. Stir in cream, parsley and salt and bring to a boil. Cook til lightly thickened, about 3 minutes. Season with salt and pepper. Remove from heat and cover to keep warm.
3Add fettuccine to boiling water and cook just til barely tender, 1 to 2 minutes. Drain in strainer. Return pasta to pot. Add sauce and Parmigiano and stir gently. Serve hot, with a bowl of grated Parmigiano passed on the side.