In frying pan, melt butter; add mushrooms and onion, stirring until
all liquid evaporates, about 5 minutes. Add seasonings and flour;
stir until blended. Gradually stir in milk and sherry. Blend in egg
yolks one at a time. In a separate bowl, beat egg whites until stiff
peaks form. Fold whites into mushroom mixture until just blended;
fold in about 4/5 of cheese. Spoon mixture into buttered individual
souffle dishes or single large souffle dish. Sprinkle remaining
cheese on top. Bake small dishes for 25-30 minutes at 375 degrees.
Bake large souffle at 350 degrees for 35- 40 minutes or until puffy
and golden. Serve immediately.
