Preheat the oven to 350F. Get out an 8.5 by 4.5-inch loaf pan (a 9 by 5-inch loaf pan will also work, but the bake time might change a little). Either butter and flour the pan, or line it with 2 pieces of parchment paper so the paper hangs over all 4 sides.
Add the mashed banana, buttermilk, oil, egg, vanilla, and brown sugar to a medium bowl and whisk well to combine.
Add the flour, cocoa powder, baking soda, salt, and instant espresso powder to a large bowl, and whisk to combine.
Add the wet ingredients to the dry all at once and stir just to combine, being careful not to over-mix. Fold in ¾ cup chocolate chips.
Transfer the batter to the prepared pan and spread it out evenly.
Bake until a toothpick inserted in the center comes out clean, about 65 to 75 minutes.
As soon as it’s out of the oven, sprinkle the remaining ¼ cup chocolate chips evenly across the top (they’ll melt on there perfectly).
Cool, and then slice and serve.
Notes:
ONLY use 3 bananas. More bananas =/= more banana flavor.
Don't bother sprinkling the chocolate chips on after it bakes. Throw the whole cup into the batter.
