Preheat the oven to 350ºF. Line one 8-inch by 4-inch by 2-inch loaf pans with a piece of parchment long enough to hang over the sides (this helps to lift the cake out of the pan easily).

In a large bowl, add the sugar, egg, tahini, oil, and vanilla. Beat with a whisk until well combined.

Add the flours, baking powder, baking soda, salt, and half of the sesame seeds. Stir with a wooden spoon or spatula, just long enough until blended, and there are no visible signs of flour in the batter (it will be stiff).

Fold the bananas into the batter.

Scrape the batter into the prepared pan. Sprinkle the remaining sesame seeds on top. Bake 45 to 50 minutes, until a metal skewer inserted in the center comes out clean. Set the pan on a wire rack, and let cool for at least one hour before slicing. The cake will stay fresh, wrapped tightly in parchment paper, for up to three days.