Step 1

Preheat oven to 350F/180C. Butter a 9×5-inch loaf pan.

Step 2

In a medium bowl, sift together flour, cocoa powder, baking soda, salt, and cinnamon. Set aside.

Step 3

In a standing mixer fitted with the paddle attachment, beat together butter and sugar on medium speed for 2-3 minutes, until light and fluffy. Scrape down the sides and bottom of the bowl as necessary. Add eggs, one at a time, beating well after each addition. Add mashed bananas and vanilla extract, and beat until combined.

Step 4

Reduce mixer to low speed and add half of the dry ingredients, beating just until combined. Add sour cream and beat until combined. Add the other half of the dry ingredients and beat just until combined. Do not overmix – the less you mix, the lighter the cake will be. Fold in the chocolate chips.

Step 5

Pour batter into prepared loaf pan and bake for 50-60 minutes, or until a toothpick inserted into the center of the cake comes out clean or with just a few moist crumbs. Let the cake cool for 10 minutes on a wire rack, then turn it out from the pan and let it cool completely.