Heat oven to 350°F. Spray 9-inch round cake pan with nonstick cooking spray; sprinkle lightly with flour.
In small bowl, combine egg whites and 1/2 teaspoon baking powder; beat until stiff peaks form. Set aside.
In large bowl, combine flour and all remaining cake ingredients; beat at low speed until moistened. Beat 2 minutes at medium speed. Gently fold stiffly beaten egg whites into batter. Pour into sprayed and floured pan.
Bake at 350°F. for 27 to 35 minutes or until toothpick inserted in center comes out clean.
In small bowl, combine topping ingredients; spread over hot cake. Cool cake in pan on wire rack for 30 minutes or until completely cooled.