In 1/4 cup hot butter in medium saucepan, sauté chopped onion and sliced mushrooms, stirring until tender.
Remove from heat: stir in flour and pepper to blend well. Gradually stir in cream. Return to heat and bring to boil, stirring constantly. Reduce heat, stir frequently, until quite thick, about 4 to 5 minutes.
Add Gruyere cheese and stir until melted.
Remove from heat. Stir in white wine, 1/2 cup court bouillon and parsley.
Add scallops and mix well.
Divide into 6 scallop shells.