Cook the pasta as directed on the package. Drain the pasta, reserving 1/2 cup of the cooking water. Keep the pasta warm. Meanwhile, in a 12-inch nonstick skillet, heat 1 tablespoon of the oil and the butter over medium heat. Add the mushrooms and cook for 5 minutes or until browned and tender, stirring frequently. Remove the mushrooms from skillet. Add the remaining 1 tablespoon of oil and garlic. Cook for 2 minutes, stirring frequently. In a glass measuring cup, stir the flour into the milk with a wire whisk until smooth. Gradually add the milk mixture to the skillet, stirring constantly. Bring to a boil; boil 1 for minute. Remove from the heat. Stir in the sour cream, 1/4 cup of the Parmesan cheese and the mushrooms. Add the cooked pasta; toss until well coated. If desired, toss in the pasta water 1 tablespoon at a time until the desired consistency is reached. Sprinkle each serving with the remaining Parmesan cheese.