Preheat your oven to 350F. Cut out two pieces of parchment paper the same size as the bottom of two 8″ or 9″ cake pans.
Place a large bowl over a pot of barely simmering water. Place the butter, dark chocolate, water, cocoa powder and sugar in the bowl and stir until the chocolate has melted. Remove from heat. Keep the pot of water nearby to use for making the frosting.
Stir the buttermilk and oil into the chocolate mixture. Whisk in the three egg yolks. Set it all aside.
Mix together the flours, baking powder, baking soda and salt. Whisk, fold or stir into the chocolate bowl until just barely combined.
Place the egg whites in the bowl of a stand or hand held mixer. Beat on medium high speed until they just start to form peaks. Fold these egg whites into the batter.
Pour the batter evenly between the two pans. Forget everything you ever heard about cake baking and avoid the urge to tap the pans (this punches down air pockets, which will lead to a denser cake).
Bake for about 35 minutes, or until the center no longer jiggles when you shake or poke it. Place the cake pans over your stove’s burners or a cooling rack and let the cakes cool in their pan for at least an hour.
Once cooled, run a butter knife or offset spatula around the edges of the pan. Flip the cakes onto a piece of parchment or your counter. Peel back the parchment paper and let the cakes cool some more.
Make the ganache:
