Wash the mushrooms under cold water. Cut into bite sized pieces. In a large skillet over medium heat, melt the butter with the onion. Sauté until golden. Add the mushrooms and cover. Cook for about 10 minutes. Add the wine and allow to cook uncovered for about 5 more minutes. Add the pancetta and mix well for a few minutes. Add the cream and allow to reduce for about 5 minutes.
Cook the pasta until al dente. Drain and add to the mushroom mixture. Mix well. Serve immediately with a sprinkle of Parmigiano.