Method:

*Use Dutch processed for a rich, dark flavor

Heat oven to 350°. Grease three 8 inch cake rounds. Combine chocolate and cocoa in  medium bowl. Pour boiling water over and whish until smooth. Sift together the flours, baking soda, and salt onto a large sheet of parchment or waxed paper; set aside.

Beat the butter at medium speed until creamy. Add brown sugar and beat on high until fluffy. Stop mixer and scrape down bowl. Add eggs,  one at a time, and beat on medium. Add sour cream and vanilla and beat until combined.

Turn mixer to low and add one third of flour mixture, followed by half of chocolate mixture. Repeat, ending with flour mixture. Beat until combined. Do not overmix.

Divide the batter evenly among cake pans. Bake until toothpick comes out clean, about 20 minutes. Cool cakes on rake. Run knife around perimeter to loosen, invert cakes and cool completely.

Assemble bottom layer on cake platter, frost, assemble middle layer, frost, assemble top layer and frost completely.