Preheat oven to 350 degrees F. Grease bottom of loaf pan. Combine sugar and butter in a large bowl and blend well. Add eggs and blend well. Stir in buttermilk. Add flour, cocoa, baking powder, baking soda, and salt; stir just until dry ingredients are moistened. Stir in nuts, if using. Pour into prepared pan.
Bake for 55-65 minutes until toothpick inserted in center of loaf comes out clean. Cool 15 minutes; remove from pan. Cool completely. Wrap tightly and store in refrigerator.