preheat oven to 350

prepare 3 each 9 inch baking pans by greasing and flouring sides of pans and placing parchment or waxed paper in bottom.

whisk cocoa, 1/2 cup flour and water in a bowl and set aside.

In another bowl combine flour, baking powder, baking soda.

In a large bowl beat remaining sugar and butter till light and fluffy.

add egg whites and egg to butter mixture. Beat in yogurt and flour mixture.

divide batter in half.

fold cocoa mixture into half of batter

spoon chocolate batter into large heavy plastic bag. Cut off corner of bag and pipe in a ring covering about 1/3 the radius around edges of TWO of the prepared pans.

fill another bag with white batter.

pipe white batter in ring inside of existing chocolate rings.

finish center with chocolates batter.

pipe white batter around edge of 3rd pan. then pipe chocolate batter inside white ring and finish center with white batter.

bake about 25 minutes till toothpick comes out clean.

Cool cakes on wire rack

place chocolate edge cake on plate and frost top with white frosting.

place white edge cake next and frost top with white frosting.

place final cake and finish frosting with chocolate frosting.