Heat the oven to 350°F (175°C). Grease a 9 x 5-inch loaf pan and line it with parchment paper, leaving a little overhang to make lifting the baked loaf easier.

Mash the very ripe bananas in a large bowl until mostly smooth. A few small soft pieces are welcome because they add pleasant banana pockets to the finished bread.

Whisk the melted and slightly cooled butter, packed light brown sugar, eggs, and vanilla into the mashed bananas. Continue whisking until the mixture looks evenly combined.

In a separate bowl, whisk together the flour, natural cocoa powder, baking soda, and salt. Breaking up cocoa lumps now helps the dry ingredients blend into the batter evenly.

Add the dry mixture to the banana mixture and stir just until no dry streaks remain. Do not overmix, since excessive stirring can make the loaf dense or rubbery.

Fold in 1/2 to 1 cup of semisweet chocolate chips, reserving a few for the top if desired. Use a gentle folding motion so the batter stays tender.

Transfer the batter to the prepared pan and smooth the surface. Sprinkle the reserved chocolate chips over the top, then bake for 55–65 minutes.

Check the center with a toothpick; the loaf is ready when the toothpick comes out with a few moist crumbs but no wet batter. Cool in the pan for 15–20 minutes, then lift the bread onto a wire rack and cool completely for the cleanest slices.