Step 1

Preheat oven to 350°F. Line a 9x5 loaf pan with parchment paper and set aside.

Step 2

In a medium bowl, whisk together the flour, cocoa powder, baking powder, and baking soda.

Step 3

In a large mixing bowl, beat the butter and sugar until light and fluffy. Beat in the egg and vanilla.

Step 4

In a separate medium mixing bowl, combine the sour cream and buttermilk.

Step 5

Add half of the flour mixture to the butter mixture. Beat to combine. Add the sour cream mixture. Mix well. Add the remaining flour mixture and mix well.

Step 6

Spread mixture into the prepared pan. Bake for 55 minutes.

Step 7

Remove from the oven to a cooling rack and allow to cool for 10 minutes in the pan. Remove from the pan and allow to cool completely on a wire rack.