In a large skillet heat butter and oil over medium heat. Add onion and garlic. Cook for 4 to 5 minutes or until onion is tender, stirring occasionally. Stir in mushrooms, thyme, 12 teaspoon salt, and 14 teaspoon ground black pepper. Cook 4 to 5 minutes more or until mushrooms are tender and lightly browned, stirring occasionally. Add cream. Bring just to boiling; reduce heat. Boil gently, uncovered, for 2 to 3 minutes or until thickened. Stir in cheese until melted.
To serve, place hot cooked pasta in serving bowl. Spoon mushroom sauce over pasta. Sprinkle with parsley. Makes 4 servings.