In a large saucepan, melt the butter over low heat. Be careful not to burn the butter.

Once the butter is melted, add the marshmallows and stir continuously until they are completely melted and smooth. Remove the saucepan from the heat.

Stir in the pumpkin pie spice and vanilla extract until well combined.

Add the Rice Krispies cereal to the marshmallow mixture. Stir gently until the cereal is evenly coated.

Grease a 9x13 inch baking pan with butter or non-stick cooking spray. Press the mixture evenly into the prepared pan using a greased spatula or wax paper. Avoid pressing too hard, which can make the treats tough.

Let the treats cool for at least 15-20 minutes before cutting into squares. Enjoy!