Preheat oven to 375 degrees.  Lightly greases a 2 quart baking dish.  Cook pasta and drain.  In a large saucepan, melt the butter and saute the mushrooms. Add the flour and cook stirring 2 minutes, slowly add the broth and half and half.  Cook and stir until thick and bubbly.  Add the chicken and shredded cheese.  Stir until cheese is melted.  Stir in the sherry, salt and pepper to taste.  Toss with the cooked pasta and pour into prepared baking dish.  Top with Parmesan cheese, bake for 15 - 20 minutes until hot and bubbly.  Top with parsley.