Instructions

Preheat the oven to 350 degrees. Lightly grease the bottom of a 9×13 baking pan. Sift the three flours together. Add cocoa, xanthan gum, baking powder, and baking soda to the flours and whisk together in a med. bowl. Beat the butter until creamy . Slowly add the brown sugar and the granulated sugar; whip until fluffy. Add the eggs and the egg yolks one at a time. Add the vanilla. Turn the mixer to low and alternately add the flour mixture and the buttermilk. Pour into the prepared pan. Bake for 30-35 minutes until the cake is springy to the touch.