In a large skillet, cook prosciutto or bacon until crisp; drain off drippings and crumble prosciutto or bacon. Set aside.Advertisement
Wipe pan clean. Cook scallions in same skillet in butter or margarine over medium heat for 2 to 3 minutes. Add mushrooms and cook for 2 to 3 minutes more. Remove skillet from heat.
In a large bowl, beat together the eggs, milk, and pepper. Stir in cheese and the mushroom mixture. Pour into a greased 2-quart rectangular (12x7-1/2x2-inch) baking dish.
Bake in a 350 degree F oven for 35 to 40 minutes or until puffed and a knife inserted off-center comes out clean. Let stand for 5 to 10 minutes before cutting. Serve warm. Makes 6 servings.
Remove and discard the tough stems from the shiitake mushrooms before slicing them.