Prepare a 9-inch square baking tin by lining it with baking paper and greasing it lightly with butter.

In a large mixing bowl, combine rice cereal and a pinch of salt.

In a medium saucepan, melt butter, marshmallows, and Biscoff spread over low to medium heat, stirring continuously.

Pour the melted mixture over the rice cereal and fold gently until combined.

Allow the mixture to set at room temperature for about 1 hour.

Melt white chocolate in a microwave-safe bowl in 30-second intervals until smooth.

Pour melted chocolate over the treats and swirl in warmed Biscoff spread.

Sprinkle crushed Biscoff biscuits on top and let them set completely for at least 30 minutes.