Line an 8x8" baking dish with parchment paper, set aside.
Add the butter, evaporated milk, and brown sugar to a large saucepan over medium-high heat. Stir well until the sugar is fully dissolved.
Bring the mixture to a rolling boil, and cook, stirring constantly, for two minutes.
Remove from heat, and add the Biscoff spread, marshmallow fluff, and vanilla extract. Mix well until the candy is smooth and creamy.
Pour the mixture into the prepared 8x8" prepared baking dish, and spread evenly.
Immediately garnish with the crushed cookies, gently press the crumbs into the top of the fudge. Allow the fudge the set at room temperature for up to one hour.
Once the fudge is set, remove it from the pan, cut into squares, serve and enjoy!