Prepare the Pan

Line a 9x13-inch baking dish with parchment paper or grease it lightly with cooking spray. Set aside.

Melt the Butter

In a large saucepan, melt the butter over low heat. Stir frequently to prevent browning.

Add Marshmallows

Once the butter has melted, add the marshmallows to the pan. Stir constantly until the marshmallows are completely melted and smooth. Remove from heat and stir in the vanilla extract, if using.

Combine with Cereal

Gradually add the Rice Krispies cereal to the melted marshmallow mixture, stirring until all the cereal is evenly coated.

Transfer to Pan

Pour the mixture into the prepared baking dish. Use a greased spatula or a piece of parchment paper to press the mixture evenly into the pan. Don’t press too firmly; this keeps the treats light and chewy.

Cool and Cut

Allow the Rice Krispie Treats to cool at room temperature for about 30 minutes. Once set, cut them into squares or rectangles and serve.