Method:

Grease bottom of 13 x 9 x 2-inch pan. Line with waxed paper then grease again. Preheat oven to 375 degrees. 

1. Combine in small mixing bowl the flour, 1/2 cup sugar, cocoa, baking powder and salt. Set aside. 

2. In large mixing bowl, beat egg whites at high speed until soft mounds form. Gradually add 1/4 cup sugar and continue beating until stiff peaks form. 

3. Combine egg yolks, water and vanilla. Add to dry ingredients and beat one minute at medium speed. Fold into the egg whites using rubber spatula. 

4. Spread mixture into prepared pan; bake for 12 to 15 minutes. Remove from pan immediately and cool. 

5. Cut cake in half crosswise to make two 9 x 6-inch layers. Spread one layer with filling. Top with bananas and place second layer on top of bananas. IMPORTANT: Chill 6 hours to overnight. 

6. Just before serving, sprinkle with sifted powdered sugar or serve with sweetened whipped cream. 

FILLING: Combine 3/4 cup sugar, cornstarch and salt in saucepan. Gradually add 2 cups milk and cook over medium heat, stirring constantly, until mixture is very thick. Blend 1/2 cup of the hot mixture into 2 eggs that have been slightly beaten; add back to saucepan. Cook 2 minutes longer, stirring constantly. Blend in margarine and vanilla. Cover and chill thoroughly before using to fill cake layers.