Preheat the oven to 350 degrees Fahrenheit. Line the bottom of a 9-inch round pan with parchment paper. Spray with non-stick cooking spray and dust with cocoa powder.
In a large bowl, whisk together the flour, baking soda, baking powder, and salt. Set aside.
Mash the bananas in a small bowl until smooth, using the back of a fork.
With an electric mixer, beat together the sugar and melted butter until fluffy. Add eggs, one at a time and beat just until smooth. Mix in the peanut butter, milk, mashed bananas, and vanilla extract.
Add the wet ingredients into the dry and mix until just incorporated. Pour the half of the batter into a separate bowl.
Melt the chocolate in a microwave-safe bowl in 30-second increments until smooth (you can also do this in a small saucepan on the stovetop over low heat). Add the chocolate and cocoa powder to one half of the batter and mix until smooth.
Alternating between the chocolate and peanut butter, drop the batter into the prepared cake pan with a spoon. Run a knife in 8-figure patterns through the batter to create swirls. Gently press banana halves into the top, if desired.
Bake for 50-60 minutes or until a toothpick inserted in the middle comes out clean. Tent the bread with a foil during the last 15 minutes of baking if necessary to prevent from burning.
Cool for 10 minutes then remove from the pan place on a cooling rack to cool completely before slicing.
It's best to use a good quality chocolate bar instead of chocolate chips. As mentioned in the post, I had dark chocolate on hand, but you can use semi-sweet as well.
For a loaf of healthier banana bread, use the whole wheat bread. I think it would be good with almond flour for a gluten-free version.
You can replace the butter with vegetable oil or coconut oil.
Drop larger mounds of batter into the pan for that marble look (not like I did by the spoon - see photos)
Using the banana on the top is optional.
You can add ½ cup chopped walnuts to the batter if you desire.