PREPARATION:

1. Preheat oven to 350°F. Spray 2-quart round baking dish with nonstick cooking spray.
2. Place bacon in single layer in large skillet; cook over medium heat until crisp. Remove from skillet; drain on paper towels. Crumble and set aside.
3. Combine sour cream, egg yolks, flour and pepper in large bowl; set aside. Beat egg whites in medium bowl at high speed of electric mixer until stiff peaks form. Stir one fourth of egg whites into sour cream mixture; fold in remaining egg whites.
4. Arrange half of spinach in prepared dish. Top with half of sour cream mixture. Sprinkle 1/4 cup cheese over sour cream mixture. Sprinkle bacon over cheese. Repeat layers, ending with remaining 1/4 cup cheese.
5. Combine bread crumbs and butter in small bowl; sprinkle evenly over cheese. Bake, uncovered, 30 to 35 minutes or until egg mixture is set. Let stand 5 minutes before serving. Garnish as desired.