Preheat oven to 350°F. Grease a loaf pan with non-stick cooking spray or grease with shortening and set aside.
Add the bananas to a bowl with the warm, melted butter and mash using a fork or potato masher.
Add the oil, buttermilk, beaten eggs, and vanilla. Mix well to combine.
In a second large bowl, whisk together the flour, cocoa powder, sugar, brown sugar, baking soda, and salt.
Pour the wet ingredients into the dry ingredients and mix together with a wooden spoon until combined (the mixture will be thick).
Fold in a ½ cup of the chocolate chips until combined into the batter.
Spoon the mixture into the prepared loaf pan and bake for 45-55 minutes or until a cake tester inserted in the center of the bread comes out clean.
While the cake is still hot, scatter the chopped chocolate over the top. Allow to cool in the pan for 10 minutes before transferring to a wire rack to cool. This cake can be served warm or at room temperature.
Notes
Be sure to follow the steps of the recipe. Mixing the wet and dry ingredients separately before combining them together helps to avoid overmixing which will result in a dense, tough cake.
Measure your flour correctly by using a measuring cup meant for dry measurements, spoon the flour into the cup and then level off the top of the cup. This ensures you’re not adding extra flour, which will dry out the cake.
To avoid the cake sticking to the pan, use a good quality, non-stick pan that’s well greased with baking spray or shortening instead of butter. Butter can actually cause sticking. When in doubt, line the pan with greased parchment paper.