Grease a 9x13 inch baking pan with butter or cooking spray to prevent the treats from sticking.

In a large saucepan over low heat, melt the unsalted butter. Stir occasionally to ensure it doesn’t burn.

Once the butter is melted, add the mini marshmallows to the saucepan. Stir continuously until the marshmallows are completely melted and smooth. This should take about 3-5 minutes.

If using, stir in the vanilla extract for added flavor.

Remove the saucepan from heat. Quickly add the Rice Krispies cereal to the melted marshmallow mixture.

Using a wooden spoon, stir the mixture until all the cereal is evenly coated with the marshmallow mixture. This step is crucial to ensure every piece of cereal is covered.

Pour the mixture into the prepared baking pan. Using a buttered spatula or your hands (lightly greased), press the mixture evenly into the pan. Make sure to pack it down firmly but gently to avoid crushing the cereal.

Allow the Rice Krispie treats to cool at room temperature for about 30 minutes.

Once cooled, use a butter knife to cut them into squares or rectangles. Serve immediately or store in an airtight container.