Preheat the oven to 325Â°F.
Butter and lightly flour a 9x5x3-inch loaf pan, or spray it with a butter-flour spray.
In a large bowl, on the medium speed of an electric mixer, cream the butter until smooth.
Add the sugars and beat until fluffy, about 3 minutes.
Add the egg and beat well, then the buttermilk and vanilla.
Sift the flour, cocoa, baking soda and salt together right into your wet ingredients.
Stir together with a spoon until well-blended but do not over mix. Scrape down the batter in the bowl, making sure the ingredients are well blended.
Pour the batter into the prepared loaf pan. Bake for 60 to 70 minutes, or until a cake tester inserted into the center of the loaf comes out clean.
Cool in pan on a rack for about 10 to 15 minutes, at which point you can cool it the rest of the way out of the pan.
Serve with fresh berries.