Preheat your oven to 350°F (175°C) to ensure even baking.
Grease a 9x5 inch loaf pan with butter or non-stick spray, or line it with parchment paper.
In a medium bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.
In a large mixing bowl, combine the mashed bananas, eggs, granulated sugar, brown sugar, and vanilla extract. Whisk until well combined.
Pour the melted butter into the banana mixture, stirring gently until incorporated.
Gradually add the dry ingredient mixture to the wet ingredients, folding with a spatula until just combined.
In a small bowl, mix the black sesame tahini and black sesame powder until smooth. Mix about a third of the banana bread batter with the black sesame mixture.
Pour half of the plain banana bread batter into the prepared loaf pan. Spoon the black sesame batter on top, then add the remaining banana batter. Swirl gently with a knife or toothpick.
Sprinkle a little extra granulated sugar over the top and bake for 55 to 65 minutes, until a toothpick comes out clean.
Let the loaf cool in the pan for about 10 minutes, then transfer to a cooling rack to cool completely before slicing.
