Line 9×13 pan with parchment paper. Butter generously. Or skip the paper and just butter the pan.
In the microwave or on the stove top, melt together caramels, condensed milk, and 1 stick (8 tablespoons) of butter over low heat. Stir, stir, stir. Keep your eyes on it or it will burn.
In a large bowl or saucepan, melt together marshmallows and 1 stick (8 tablespoons) of butter. Stir in cereal.
Drop big spoonfuls of the marshmallow cereal mixture into the pan – only use half of the mix. Spray the back of a large spoon with cooking spray and use it to press the cereal into an even layer.
Pour caramel over the layer.
Drop spoonfuls of the remaining cereal on top of the caramel. Use the greased spoon again to press the cereal into an even layer.
Let set at least four hours before cutting into squares. Eat within a day or two.