Preheat oven to 350. Combine both flours, baking soda and baking powder and set aside.
CAKE: Beat eggs in a large mixer bowl and add sugar, stirring to mix. In a seperate bowl, combine buttermilk and oil, mixing well. Add flour mixture and buttermilk mixture alternately to egg mixture, beginning and ending with flour mixture, beating well after each addition. Stir in vanilla. Pour 2/3 cup batter into greased and floured round cake pans (I use 8" pans). Bake at 350 for 8 minutes or until layers begin to brown around edges. Allow to cool in pans 5 minutes, remove cake from pans and stack layers, placing a paper towel between each layer. Repeat with remaining batter until 10 layers are baked. PLEASE NOTE: Prepare icing after layers are baked.
ICING: Combine sugar & cocoa in a large heavy saucepan. Add milk & combine well. Cook over medium heat, stirring constantly until sugar melts. Add butter, stirring until melted. Allow to come to a boil then continue boiling for 7 minutes. Remove from heat then add in vanilla. Icing will be thin at this point but will harden later. Ice cooled layers while icing is warm.
ASSEMBLE: Start stacking layers and be generous with icing between layers because there is plenty. Once last layer is on top, ice generously. Icing will run down the cake, which actually will ice the sides. Keep spooning icing back on top as it puddles.
Note: the icing will start to get gooey as it cools but then will harden later. This cake is better made the day before serving. This allows the icing to harden properly. If you can't make it a day ahead, make it in the morning to serve that evening.