Preheat your oven to 325°F (163°C) and prepare a large loaf pan by greasing it or lining it with parchment paper.

In a mixing bowl, combine the crushed Biscoff cookies, brown sugar, and cinnamon for the crumb topping, then mix well. Add cubed cold butter and blend until coarse.

In a stand mixer, beat the room temperature unsalted butter until creamy, then gradually add the granulated sugar, mixing for 3 minutes until light and fluffy.

Add the eggs one at a time, mixing well. Fold in the mashed bananas and vanilla extract.

Slowly add the flour, baking soda, and salt to the wet mixture on low speed until no dry ingredients are visible.

Pour half of the banana batter into the loaf pan, smoothing with a spatula.

Drizzle the melted cookie butter over the first layer of banana batter, then spoon the remaining batter on top.

Sprinkle the reserved crumb topping evenly over the batter.

Bake for 60-65 minutes, testing for doneness with a toothpick; it should come out clean with a few moist crumbs.

Let the bread cool in the pan for 10-15 minutes, then transfer to a wire rack to cool completely.