Preheat oven to 425°F (220°C).

Grease and line a loaf pan with parchment paper.

In a large bowl, add bananas and mash until smooth with a few chunks.

Add melted butter, brown sugar, granulated sugar, eggs, and mix until smooth.

Add sour cream and vanilla extract. Mix until fully combined.

In a separate bowl, whisk together flour, cocoa powder, baking soda, and salt.

Fold dry ingredients into wet ingredients just until combined.

Gently fold in chocolate chips.

Pour batter into prepared loaf pan and smooth the top. Add extra chocolate chips if desired.

Bake at 425°F for 10 minutes, then reduce oven temperature to 350°F (175°C) without opening the oven door.

Continue baking for 45–55 minutes, loosely tenting with foil around the 40-minute mark if the top is browning too quickly.

A toothpick inserted into the center should come out with moist crumbs, not wet batter.

Let cool in the pan for 15 minutes, then transfer to a wire rack to cool completely before slicing.