1. Prepare pasta according to package directions.
2. While pasta is cooking, wipe all the mushrooms
clean with a paper towel.
3. Trim the stem end from the mushrooms. (Remove all
of the stems if you are using shitakes).
Slice mushrooms 1/4-inch thick.
4. Melt the butter or margarine over low heat in a
large skillet with a tight fitting lid.
5. Add mushrooms and parsley, cover skillet and let
mushrooms cook until they are completely
tender and have released their liquid, about 15
6. Check the mushrooms once or twice during cooking
to make sure they are not browning.
7. Whisk the sour cream and milk in a small bowl
8. Just before draining the pasta, mix 1/4 cup of
the pasta cooking water into the sour cream
9. Drain the pasta and transfer it to the skillet.
10. Add the sour cream mixture and heat to boiling.
Add salt and pepper to taste.
11. Boil together one minute, tossing pasta to coat
with sauce and to evenly distribute mushrooms.
12. Divide pasta between 2 plates, spooning extra sauce on top.