Preheat oven to 350°F. Grease a 9×5 inch loaf pan and line with parchment paper.
In a large bowl, mash bananas until mostly smooth with just a few small chunks.
Whisk in Biscoff spread, oil, eggs, vanilla, and sour cream until well combined and glossy.
In a separate bowl, combine flour, baking soda, salt, cinnamon, and sugar.
Pour dry ingredients into wet and stir just until no flour streaks remain. Do not overmix.
Pour half the batter into prepared pan. Dollop spoonfuls of extra Biscoff spread over the top, then add remaining batter.
Use a knife to swirl through the layers creating marbled effects. Sprinkle crushed Biscoff cookies on top if desired.
Bake for 55 to 65 minutes until a toothpick inserted in center comes out with just a few moist crumbs. Tent with foil after 30 minutes if top browns too quickly.
Cool in pan for 10 minutes before transferring to a wire rack to cool completely.