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 continuously until fully blended and smooth.
03 - Add mini marshmallows to the saucepan and stir constantly until melted and fully combined with the mixture.
04 - Remove the pan from heat. Gently fold in the Rice Krispies cereal, ensuring all pieces are evenly coated.
05 - Transfer the mixture to the prepared pan. Use a greased spatula or wax paper to press the mixture gently and evenly into the pan.
06 - Drizzle the melted Biscoff spread over the surface and scatter crushed Biscoff cookies if using.
07 - Allow the prepared treats to cool at room temperature for 45 minutes or until firm. Cut evenly into 16 squares before serving.