1. Melt the butter in a large saucepan on low heat. Once melted, add the marshmallows, white chocolate chips and vanilla. Continue to cook until everything is melted and smooth.
3. Remove from the heat, add the Rice Krispies and stir until everything is well coated.
4. Place in a 13×9 pan coated with nonstick spray. Using a non stick spray coated spatula or parchment paper, press the Rice Krispie treats to fill the pan. Cool, then cut into squares.