Preheat the oven to 350°F (175°C). Grease or line a 9×5-inch loaf pan with parchment paper.
Mix dry ingredients: In a bowl, whisk together flour, baking soda, salt, and cinnamon. Set aside.
Cream butter & sugar: In a large bowl, beat softened butter and sugar until fluffy. Add eggs one at a time, then mix in vanilla.
Stir in mashed bananas and Biscoff cookie butter until smooth.
Combine wet & dry: Alternate adding the flour mixture and milk, mixing just until combined (don’t overmix).
Bake: Pour batter into the prepared loaf pan. Optionally, swirl extra Biscoff on top. Bake for 50-60 minutes, or until a toothpick comes out clean.
Cool & decorate: Let cool for 10 minutes in the pan, then transfer to a wire rack. Drizzle with melted Biscoff and sprinkle crushed cookies on top.