Blanch the Brussels sprouts for 5 minutes in a stock pot of salted, boiling water.
Remove, cool and halve lengthwise.
In a large heavy skillet add 1/8 cup of oil and oyster mushrooms on medium high.
Add a pinch of salt and cook until browned, (7 minutes)
Add more oil, up to 1/8 cup and and shallot, 1 minute
Place sprouts in the skillet cut side down to brown, 2 or 3 minutes
Add sherry and boil to reduce by half., 3 minutes
Add cream and simmer until it thickens, 3 minutes, stirring gently
Stir in lemon juice and zest.
Add salt if necessary and serve