Prepare the baking pan as noted above.
In a large microwave safe bowl (I love these pyrex bowls) melt the unsalted butter on medium heat.
Remove the bowl and add the marshmallows, stirring them in until you have a melted marshmallow mixture.
Quickly stir in the rice krispies cereal until well blended.
Then using a greased spatula, spread the cereal mixture into the bottom of the pan that’s been prepared with wax paper and non-stick spray.
Be careful not to pack the cereal mixture too tightly, as this will make the krispy treats harden.
We like to drizzle melted chocolate on top.
Cut into squares and store in an airtight container.