Preheat oven to 350. Prepare two 9" cake pans with cooking spray and line with parchment paper. Set aside.
In a bowl combine the cocoa powder and the unsweetened chocolate.
Pour the boiling water over this mixture and whisk until smooth. Set aside to cool.
In another bowl, sift together the flours, baking soda, and salt, set aside.
Beat the butter in the bowl of a stand mixer fitted with a paddle attachment on medium until light and fluffy.
Add the brown sugar and beat on high for 3 minutes until light and fluffy.
Scrape the sides of the bowl, then add the eggs one at a time on medium speed.
Add the sour cream and the vanilla and mix 1 minute.
Add the 1/3 flour mixture, 1/3 chocolate mixture, repeat with 1/3 of each, then again ending with the flour mixture.
Beat just to combine, do not over mix.
Remove bowl from mixer and scrape the sides to be sure everything is combined.
Pour batter into prepared pans.
Bake for 20-23 minutes or until a toothpick comes out clean.
.Remove to wire rack and let cool in pan for 15 minutes.
Remove from pans and let cool completely.
Once cooled frost with your favorite frosting