Preheat oven to 375°F / 200°C. Grease a 20 cm / 8x4-inch loaf pan with butter, and line the base and sides with baking paper.
In a medium bowl, whisk together the tahini and orange juice. Stir in banana slices and sesame seeds, separating the banana slices as you add them so they don’t clump together. Set aside.
Place butter and sugar in the bowl of a stand mixer fitted with the paddle attachment and beat on medium-high speed for about 3 minutes, until light and fluffy. Add the eggs, one at a time, until combined, scraping down the bowl as needed.
In a separate bowl, whisk together the flour, baking powder, and salt. Add to the stand mixer bowl and mix on low speed, just to combine, about 30 seconds.
Add the tahini-banana mixture to the bowl with the speed still on low and mix until combined. Pour the batter into the prepared pan and smooth the top.
Bake for 25-30 minutes, until golden brown. Without removing it from the oven, carefully cover the bread loosely with foil. Continue to bake for an additional 25-30 minutes, until the bread is cooked through and a skewer inserted in the centre comes out clean. Remove from the oven and set aside to cool in the pan.
Meanwhile, make the frosting: place all ingredients in the bowl of a stand mixer fitted with the whisk attachment. Whisk for 2 minutes on medium speed until combined and airy, scraping down the sides of the bowl as needed to mix thoroughly. Set aside until the cake has cooled.
Make the caramelized banana: heat the oven broiler on its highest setting, with a rack placed about 10 cm beneath the heat source. Arrange banana slices on a baking sheet and sprinkle with sugar. Broil for 2-3 minutes until the sugar has melted and caramelized. Remove from oven and set aside to cool.
Assemble: remove bread from the pan and transfer to a serving plate. Spread the frosting generously over the top and arrange the caramelized bananas on top. Drizzle with molasses and serve.