Prep the pan: Line an 8x8-inch (20x20 cm) baking pan with parchment, leaving overhang for easy lifting. Lightly grease the parchment.

Melt the base: In a microwave-safe bowl, combine white chocolate chips and sweetened condensed milk. Microwave in 20–30 second bursts, stirring between each, until mostly melted and smooth. Don’t overheat.

Add the Biscoff: Stir in the cookie butter until fully blended and glossy. The mixture should be thick but pourable.

Fold in crunch: Gently fold in the crushed Biscoff cookies, reserving a small handful for topping if you like.

Pour and level: Scrape the mixture into the prepared pan. Smooth the top with a spatula. Sprinkle remaining cookie crumbs on top and press lightly.

Chill to set: Refrigerate for 2–3 hours, or until firm enough to slice cleanly. For quicker setting, place in the freezer for 45–60 minutes.

Slice and serve: Lift the slab out using the parchment. Warm a sharp knife under hot water, wipe dry, and cut into small squares.