Wash the mushrooms carefully, trim the stems and thinly slice ( a food processor works well)
Peel and finely dice the onion.
Bring he chicken broth to a boil, add the mushrooms and onion Return to a boil, then turn down the heat to maintain a steady slow simmer. Add the salt, pepper and tabasco. Allow the mushroom mixture to simmer 30 to 40 minutes.
Slowly melt the butter, using a pan large enough to also hold the flour and milk. As soon as the
butter is melted, beat the flour into it with a wire whip, a ittle at a time. Leave the burner on, as you
want to gently cook the flour and butter together for about 2 minutes. This is called roux.
As you are making he roux, bring the milk to a boil in another pan. As soon as the milk reaches a boil, pour it all at once into the roux
Immediately begin beating the milk/roux with the wire whip. Steady consistent strokes are more importand than speed or force. The sauce will at fidrst look curdled, then lumpy, but the longer you beat it, the smoother it will get. It will take 2 to 4 minutes of steady beating to produce a creamy white sauce.
Cmbine the smooth white sauce with the mushroom broth and then add the cream. Add sherry
if you wish, but not until jest before serving