Preheat the oven to 325 degrees Fahrenheit. Mash the bananas in a bowl. Set aside. In a large mixing bowl, add extra-virgin olive oil, tahini, granulated sugar, and brown sugar. Whisk thoroughly.
Whisk in the eggs. Add the vanilla extract and buttermilk. Add the baking soda and salt, then with a spatula, gradually mix in the flour. Make sure to scrape the sides. Stir the ingredients until just combined. Do not over-mix!
Cover the loaf pan with parchment paper, then pour the batter in. If using a glass loaf pan, bake for 80-85 minutes. If using a metal pan, bake for 70-75 minutes. The banana bread will be done when you stick a toothpick in the center and moist crumbs stick to it. If wet batter sticks to the toothpick, it needs to bake longer.
Allow the banana bread to cool on a cooling rack for 10-15 minutes before cutting into slices and serving. Top the slices with butter. Enjoy!