Melt butter in skillet.
Saute chopped onion and sliced mushrooms over medium heat until soft.
Add shrimp and cook, stirring occasionally, until shrimp turns pink, being careful not to overcook.
Dissolve cornstarch in wine and add to skillet, along with salt, Worcestershire Sauce and cayenne, if desired. Stir over low heat until sauce thickens.
Serve over thin noodles or rice. Garnish with parsley.
Serves 4 to 6.