1. Preheat oven to 350°F (180°C).
2. In a bowl, combine mashed bananas, egg yolks and honey. Whisk until well combined.

3. In a separate bowl, combine cocoa powder, arrowroot starch, baking powder, and salt. Whisk well to break up any clumps.

4. Add the banana mixture to the dry ingredients. Whisk until everything is well combined and you have a smooth chocolate batter.

5. In a clean bowl, beat the egg whites with an electric mixer until medium peaks form. The egg whites should hold their shape but should not be very stiff. This makes them easier to fold into the batter.

6. Add about one-third of the whipped egg whites to the chocolate banana mixture and gently fold them in. Add the remaining egg whites and continue folding gently until combined. Try not to overmix so the batter stays light.

7. Line a small glass baking dish with parchment paper. I used a 4.1-cup (970 ml) glass dish that measures about 4 x 6 inches at the bottom and 5 1/4 x 7 inches at the top. 
Here's an easy trick for lining a small baking dish: turn the dish upside down and place a piece of parchment paper over it. Fold the paper around all four corners to form the shape of the dish. Turn the dish back over and place the shaped parchment paper inside. It fits much easier this way.
8. Pour the chocolate banana batter into the prepared baking dish and spread it evenly.

9. Peel the remaining banana and cut it in half lengthwise. Place both banana halves on top of the batter, cut side up, and gently press them just slightly into the batter.

10. Bake in the preheated oven for about 35-40 minutes, or until the center is set. Insert a toothpick into the chocolate part of the loaf, away from the banana topping. A few moist crumbs are fine. Let the chocolate banana cake cool before removing it from the baking dish.

Once cooled, slice and serve. Enjoy!