To a blender add 8 biscoff cookies, vanilla ice cream, milk, and biscoff cookie butter.
Blend until smooth.
Pour into a milkshake glass and top with whipped topping (optional), the remaining crushed biscoff crumbs, and melted cookie butter. Serve immediately.
Notes
Put the cookie butter into the blender last. This will prevent the Biscoff spread from sticking to the bottom of the blender.