
Preheat the oven to 400°F. Grease your baking pans with butter, or line them with parchment paper for easier removal.


Peel the overripe bananas and add them to a mixing bowl with the brown sugar. Mix on low speed until the bananas begin to break down, then increase to medium and beat until mostly smooth.



Add the melted butter, eggs, vanilla extract, and sour cream to the banana mixture. Mix just until the wet ingredients are fully combined.


In a separate bowl, sift together the flour, baking powder, baking soda, espresso powder, and salt. Fold in the chocolate chips so they are lightly coated with the dry mixture.


Add the dry ingredients to the wet ingredients and mix on low speed just until no streaks of flour remain. Avoid overmixing, which can make the cake dense.



Divide the batter between the prepared pans, filling each about halfway. Bake at 400°F for 15 minutes, then reduce the oven temperature to 350°F and bake for 20 to 30 minutes more, or until the top feels firm and a toothpick inserted in the center comes out clean or with a few moist crumbs.
Let the cake cool in the pan for 10 to 15 minutes before removing. Cool completely before slicing for the cleanest texture.