Preheat the oven to 350 degrees F. Butter a 9 x 5-inch bread loaf pan.
Add all-purpose flour, unsweetened cocoa powder, baking soda, baking powder, and fine sea salt to a small mixing bowl. Whisk to combine. Set aside.
Add unsalted butter and light brown sugar to stand mixer. Beat on medium speed, using paddle attachment, until light and creamy, about 4 minutes.
Add eggs one at a time. Beat on low speed after each addition, until fully incorporated, about 30 seconds.
Add ripe bananas to small bowl. Mash with the back of a fork. Add to stand mixer with sour cream and vanilla bean paste. Beat on low speed until fully incorporated, about 30 seconds.
Remove the bowl from the stand mixer. Fold in the flour mixture, just until incorporated. Fold in the chocolate chips. Avoid over mixing.
Pour the bread batter into the prepared bread loaf pan. Smooth into the corners with an offset spatula.
Top with slices of ripe banana. Bake in preheated oven for 65 to 70 minutes, or until a toothpick inserted in the center comes out clean.
Remove bread pan from oven and place on wire rack to cool. Run a knife along the edges of the bread pan to loosen the loaf. Invert, and remove bread from pan.
Cut loaf into individual slices. Serve warm or at room temperature.