Preheat oven to 350F. Lightly grease two 9-in loaf pans. Set aside.
In a large bowl, whisk sugar and butter until smooth. Whisk in eggs, mashed banana, buttermilk, yogurt, and vanilla until combined.
In a separate medium bowl, combine flour, cocoa, baking powder, baking soda, and salt. Combine flour mixture with liquid, gently folding until just combined.
Scrape batter into prepared pans and smooth tops. Bake bread at 350F 40-45 minutes or until a toothpick tests done. Cool bread on a wire cooling rack completely before removing from pan.
Notes
Store bread in an airtight container at room temperature up to 4 days. Bread may also be frozen up to 1 month.