Melt the butter and marshmallows together in a bowl or pot. You can do this on low on the stove or in short increments in the microwave.
Add in your Peanut Butter and stir thoroughly.
Mix in your Rice Krispies Cereal. Make sure it is evenly mixed.
Spread your mixture evenly into the 9x13 pan. Make sure it as well as the spatula are greased.
Once cooled, cut and enjoy.