Preheat oven to 350F and grease and flour a 9x5 inch loaf pan. (Optional: For easy release, you can line the pan with parchment paper so that you have a couple of inches on the sides to lift it out of the pan later. See photos.)
In a large mixing bowl, (using a stand mixer or hand mixer), cream together the butter and sugar on medium speed until lightened and fluffy. Next, add the eggs, mixing until blended.
Mix in the mashed bananas and vanilla, mixing on low to medium speed just until blended.
*In another bowl, whisk together your remaining dry ingredients: flour, cocoa powder, baking soda, and salt.
With the mixer on low speed, add the dry ingredients to the wet ingredients, and mix *just until blended*. The batter will be lumpy because of the bananas. Be careful not to over-mix.
Fold in the chocolate chips and scoop batter into the prepared (lined if applicable) pan. Sprinkle 1/4 cup chocolate chips over the top.
Bake for 55-60 minutes or until an inserted toothpick comes out clean or with just a few moist crumbs attached. *Baking times may vary. Once finished, allow to rest in the pan on a cooling rack for 5 minutes before removing. Gently pull each side of the parchment paper to pull the bread out of the pan, and rest on the cooling rack.
Serve warm, or enjoy at room temperature! Store the cooled cake in an airtight container or under a cake dome at room temperature. Or you can wrap and freeze for up to three months!