01 - Preheat oven to 350°F. Grease and flour a 9x5-inch loaf pan or line with parchment paper.
02 - Whisk together flour, cocoa powder, baking soda, and salt in a medium bowl. Set aside.
03 - Combine mashed bananas, melted butter, sugar, eggs, vanilla extract, and espresso in a large bowl. Whisk until smooth.
04 - Gradually fold the dry ingredients into the wet mixture until just combined. Do not overmix.
05 - Gently fold in the chocolate chips until evenly distributed.
06 - Pour the batter into the prepared loaf pan and smooth the top with a spatula.
07 - Bake for 50 to 60 minutes, or until a toothpick inserted into the center comes out with moist crumbs but not wet batter.
08 - Allow to cool in the pan for 10 minutes, then transfer to a wire rack to cool completely before slicing.