1. Heat oven to 350°F. Grease 8- or 9-inch baking pan.
2. Place bananas, chocolate spread, corn syrup, buttermilk, vanilla and egg whites in blender container. Cover; puree until smooth. Set aside.
3. Stir together flour, granulated sugar, baking soda and salt in medium bowl. Gradually add banana mixture to flour mixture, beating with whisk until smooth. Pour batter into prepared pan.
4. Bake 25 to 30 minutes or until wooden pick inserted in center comes out clean. Cool completely in pan on wire rack. Just before serving, sift powdered sugar over top. Cut into bars. About 16 servings.
*To sour milk: Use 1/2 teaspoon white vinegar plus milk to equal 1/4 cup.