Lightly grease a 9x13 pan with 1 tablespoon of butter.
Melt butter in large saucepan over medium heat. Add marshmallows and stir until melted. Remove from heat.
Add cereal. Stir until incorporated.
If desired, add by tablespoons full of marshmallow creme and stir slightly. You want to see pockets of fluff.
Using the back of a large spoon sprayed with cooking spray, spread cereal mixture into a 9x13 pan. Cool to room temperature. Cover. Store at room temperature.