01 - Line a 9x9-inch square pan with parchment paper and lightly grease the surface.
02 - In a large saucepan over low heat, melt unsalted butter. Add Biscoff spread and stir until fully combined and smooth.
03 - Add mini marshmallows to the butter and Biscoff mixture, stirring constantly until melted and thoroughly incorporated.
04 - Remove saucepan from heat and fold in Rice Krispies cereal, mixing thoroughly until all cereal is evenly coated.
05 - Using a greased rubber spatula or wax paper, gently press the mixture into the prepared pan to create an even layer.
06 - Drizzle melted Biscoff spread over the surface and sprinkle with crushed Biscoff cookies if using.
07 - Allow to cool at room temperature for 45 minutes or until fully set.
08 - Slice into 16 even squares and serve as desired.