Stellar Mushroom Sauce

From the Moosewood Cookbook. I love mushrooms and anything, so this sounds awesome!

2 oz. Dried Chinese black mushrooms
OR
¾ lb. Fresh shiitake, oyster and/or chanterelle mushrooms, chopped
2 Tbsp. margarine
1 lb. Domestic white mushrooms, chopped
1 cup minced onion
1 tsp. Salt
6 Tbsp. dry sherry or 3 Tbsp. balsamic vinegar
3 Tbsp. flour
1 large clove garlic, minced
¼ cup rice milk
2 Tbsp. rice milk powder or Dari-Free powder
1 lb. Fettucini or other noodles

If using dried mushrooms: Place the mushrooms in a small bowl. Add 3 cups boiling water, cover with a plate and let stand 30 minutes. Drain the mushrooms, squeezing out and saving all the liquid. Beware of sand and sediment on the bottom of the bowl when using liquid later. Remove and discard the stems, coarsely chop the mushrooms. Measure out 2/3 cup of the liquid for the sauce.

Put pasta water on to boil.

Melt the margarine in a deep skillet. Add all mushrooms, onion and salt. Cook uncovered over medium heat for about 10 minutes.
Stir in sherry (or vinegar). Turn heat to low and have a whisk ready. Slowly sprinkle in the flour, whisking steadily. Keep whisking for a minute or two after all the flour is in.
Add garlic and continue to cook and stir over low heat another 5-10 minutes. Dissolve powdered milk into liquid rice milk and add to sauce, mixing well until it is completely incorporated. Add to cooked pasta and serve.