Prepare pasta according to package directions; drain.
Remove brown gills from undersides of mushroom caps using a spoon, and discard gills. Chop mushrooms.
Melt butter in a large saucepan over medium heat; add mushrooms and garlic, and sauté 5 to 6 minutes or until tender. Stir in cream and milk. Bring to a boil over medium-high heat; reduce heat, and simmer, whisking constantly, 10 minutes. Stir in cheese, pepper, and salt; stir constantly until cheese melts and mixture thickens. Stir in 2 tablespoons parsley. Serve over hot cooked pasta. Garnish, if desired.