Directions

• Preheat oven to 350 F. Using a nonstick vegetable spray, spray a 10-inch fluted quiche pan or pie plate.
• Filling: In a large skillet heat margarine until melted. Add onion; cook over medium-low heat, stirring occasionally, until onion is just softened, about 3 minutes. Add mushrooms and dry Sherry; cook, stirring frequently, until liquid has evaporated, 15 to 18 minutes; set aside.
• CrustIn the container of an electric blender place milk, flour, egg whites, egg, thyme, salt and black pepper. Blend on high speed, until well beaten, 1 to 2 minutes. Pour 1 cup mixture into prepared pan forming a thin layer; set remaining mixture aside. Bake until firm to the touch, about 10 minutes.
• Remove from oven; transfer to a baking sheet; spoon mushroom mixture from skillet evenly over crust reserving 1/4 cup mushrooms for garnish; sprinkle with Parmesan cheese. Whirl remaining milk mixture in blender to combine; pour over cheese. Bake until puffed and brown, about 45 minutes.
• Remove from oven; allow to cool, about 10 minutes before serving (clafouti will lose some of its puffiness and flatten out). Garnish with reserved 1/4 cup mushrooms and fresh thyme springs, if desired. Serve warm or at room temperature.