Brush inside of pie shell with egg white, refrigerate. Wash the mushrooms, remove stems and chop coarsely and set the stems aside. Toss the mushroom caps in lemon juice. Cook the caps in butter in medium skillet and drain on paper towels.
Make the filling: In remaining fat in skillet, sautÚ the onion and the chopped mushroom stems, stirring, about 5 minutes. Add broccoli, parsley, 1/2 teaspoon of salt and a dash of pepper, mix well. Remove from heat. Preheat oven to 375║F. Sprinkle cheese over bottom of pie shell. In a medium bowl, with wire whisk or rotary beater, beat eggs with half and half, 1/4 teaspoon of salt, nutmeg and pepper just until combined, but not frothy. Spoon 1 rounded tablespoon of broccoli mixture into each mushroom cap. Turn the rest of the broccoli mixture into bottom of prepared pie shell over grated cheese. Pour the egg mixture over all. Arrange the 8 stuffed mushrooms on top. Place on lower rack and bake in oven 40 - 45 minutes or until puffy and golden. Remove to wire rack, cool for 10 minutes before serving. Makes 8 servings