Preheat your oven to 350°F (175°C). Grease a 9 x 5 inch loaf pan and line it with a parchment sling so the bread lifts out easily. Little step, big payoff.
In a large bowl, mash the bananas until mostly smooth. A few soft bits are fine. Whisk in the melted butter, brown sugar, granulated sugar, eggs, and vanilla. Pause for a second… it should smell like banana pudding right now.
In a separate bowl, whisk the flour, cocoa powder, baking soda, and salt. If using espresso powder, add it here so it disperses evenly.
Stir the dry ingredients into the wet, about 2 or 3 additions. Fold just until you no longer see streaks of flour. Batter will be thick. No need to overthink it.
Fold in the sour cream or yogurt, then the chocolate chips and nuts if using. A few gentle turns with a spatula. That’s it.
Scrape the batter into the prepared pan, smoothing the top. If you saved a few chips, sprinkle them on now for a pretty top.
Bake on the center rack for 55 to 65 minutes, until a toothpick inserted in the center comes out with a few moist crumbs. If it looks wet, give it another 5 minutes and check again.
Cool in the pan for 15 minutes, then lift out and cool on a rack. Warm slices are wonderful… but if you can wait until it’s just barely warm, the crumb sets beautifully.