START pasta cooking according to package directions.
In a large skillet over medium heat, MELT butter with oil; ADD onion and garlic; COOK until onion is tender, about 5 minutes, STIRRING occasionally.
STIR in mushrooms, thyme, salt and pepper; COOK until mushrooms are tender and lightly browned, about 5 minutes, STIRRING occasionally.
ADD cream and sherry (if desired); BRING just to boiling; REDUCE heat.
BOIL gently, uncovered, until thickened, about 3 minutes; STIR in cheese until melted.
Place hot cooked pasta in a serving bowl. Spoon mushroom sauce over pasta. Sprinkle with snipped fresh parsley.
Per Serving (excluding unknown items): 444 Calories; 27g Fat (55.1% calories from fat); 12g Protein; 38g Carbohydrate; 3g Dietary Fiber; 72mg Cholesterol; 558mg Sodium. Exchanges: 2 Grain(Starch); 1/2 Lean Meat; 1 1/2 Vegetable; 0 Non-Fat Milk; 5 Fat.