Preheat oven to 350 degrees F. Coat a 9-by-13-inch baking pan with cooking spray.Advertisement
Melt chocolate in a small bowl over hot (not boiling) water or in a microwave oven on Medium. Set aside.
Stir together flour, cocoa and salt in a medium bowl. Whisk together egg whites and eggs in a large bowl. Add sugar, corn syrup, applesauce, oil and vanilla. Whisk in the chocolate. Add the flour mixture to the egg mixture and stir with a wooden spoon until blended.
Pour into the prepared pan and sprinkle with walnuts. Bake until a cake tester inserted in the center comes out clean, 30 to 35 minutes. Let cool in the pan on a rack. Cut into squares.
Tip: To toast chop nuts: Place in a small dry skillet and cook over medium-low heat, stirring constantly, until fragrant and lightly browned, 2 to 4 minutes.
1 1/2 other carbohydrate, 1/2 fat