Line a 9x9-inch baking dish with foil and lightly coat it with cooking spray.

In a large saucepan, melt the butter over medium heat, then bring it to a boil. Once it starts boiling, swirl the pan constantly until the butter passes the foamy phase and becomes a deep amber color.

Immediately add the marshmallows and continue stirring until the marshmallows are melted. Remove the pan from heat.

Quickly stir in the potato chips, pretzels, popcorn and make sure to coat them in the melted marshmallows.

Transfer the mixture immediately to the prepared dish, pressing it evenly but without packing the mixture too tightly.

Allow the mixture to cool, then cut into squares.