Spray a 9x12-inch pan with cooking spray and set aside.

Heat a large saucepan on low heat.

Melt the light butter spread, ensuring to coat the bottom of the pot to prevent sticking.

Add marshmallows and melt on low flame, stirring constantly until completely melted.

Remove from heat and add Rice Krispies cereal. Stir until evenly coated and combined quickly.

Transfer the mixture into the prepared pan. Press down evenly with wax paper.

Allow to cool and set before cutting into 16 squares.