1 cup whole-wheat flour
1 cup unbleached all-purpose flour
3/4 cup Splenda Sugar Blend for Baking
1/2 cup unsweetened cocoa powder
2 teaspoons baking soda
4 large overly ripe bananas, mashed
1/2 tablespoons plain lowfat yogurt
2 egg whites
2 teaspoons vanilla extract
3/4 cup walnuts, chopped
Vegetable-oil cooking spray

Frosting
1 cup lowfat milk
3/4 cup Splenda Sugar Blend for Baking
1/2 cup unsweetened cocoa powder
1/4 cup cornstarch
1 tablespoon butter
2 teaspoons vanilla extract
Preheat oven to 350°F. Combine flours, Splenda, cocoa, and baking soda. Add bananas, yogurt, egg whites, vanilla, and 1/2 cup walnuts. Stir. Coat a 9" x 13" cake pan with cooking spray. Pour batter into pan, spreading evenly. Bake about 35 minutes. Cool.
For frosting
Raise oven to 375°F. Toast remaining 1/4 cup walnuts 6 minutes. To make frosting, pour 1/4 cup milk into a medium saucepan over medium heat. Stir in Splenda, cocoa, and cornstarch. Slowly add remaining 3/4 cup milk and bring to a low boil, stirring continuously until thick. Remove from heat and stir in butter and vanilla. Cool and spread over cake. Sprinkle walnuts over cake.