1. Line a 9 x 13 x 2 inch baking pan with foil and spray with nonstick cooking spray.
2. In large saucepan melt butter over low heat. Add in 5 cups of marshmallows and stir until completely melted. Add in the Biscoff Spread and continue stirring until the mixture is smooth. Remove from heat and stir in vanilla extract.
3. Add crisped rice cereal; stirring until well coated. Fold in the chopped Biscoff cookies and remaining 3/4 cup marshmallows.
4. Using a buttered spatula, press the mixture into the prepared pan. Cool. Cut into squares.