01 - Line a 9x9-inch square pan with parchment paper and lightly grease the surface.
02 - In a large saucepan over low heat, melt the unsalted butter. Add the Biscoff spread and stir until thoroughly blended.
03 - Add the mini marshmallows to the saucepan and cook, stirring constantly, until melted and fully combined with the mixture.
04 - Remove the saucepan from heat. Gently fold in the Rice Krispies cereal, ensuring the mixture coats the cereal evenly.
05 - Transfer the mixture to the prepared pan. Using a greased spatula or wax paper, press the mixture evenly and gently into the pan.
06 - Drizzle melted Biscoff spread evenly over the surface and, if desired, sprinkle with crushed Biscoff cookies.
07 - Allow the pan to cool at room temperature for approximately 45 minutes, or until the squares are set.
08 - Cut into 16 equal squares and serve as desired.