Preheat oven to broil.

Sauté mushrooms and onions in 3 Tablespoons butter in a large skillet until tender, about 5 minutes. Add scallops, wine, parsley, lemon juice, salt and pepper; cover and cook over medium heat 3 minutes. Drain scallop mixture, reserving 1 cup liquid. Set aside.

Melt 3 Tablespoons butter or margarine in a heavy saucepan over low heat; add flour, stirring until smooth. Cook 1 minute, stirring constantly. Gradually add half and half; cook over medium heat stirring constantly, until mixture is thickened and bubbly. Beat egg yolks until thick and lemon colored. Gradually stir about one-fourth of hot mixture into egg yolks; add to remaining hot mixture, stirring constantly. Gradually stir in reserved scallop liquid (¾ cup plus 2 Tablespoons); fold in scallop mixture. Spoon mixture into 6 greased individual baking shells.

Combine breadcrumbs and 1 Tablespoon butter or margarine; sprinkle evenly over scallop mixture in shells. Place shells on a large baking sheet. Broil 3 to 5 minutes or until top is browned and bubbly. Yield: 6 servings.