In a large saucepan over medium heat, melt the unsalted butter until it’s completely liquid. Once melted, add 5 cups of the miniature marshmallows to the pan. Stir continuously until the marshmallows are fully melted and the mixture is smooth.
Once the marshmallows are melted, remove the saucepan from the heat. Stir in the creamy peanut butter and the pure vanilla extract until well combined. The mixture will be thick and creamy, with a delicious peanut butter aroma.
Next, add the crisped rice cereal to the melted mixture. Use your wooden spoon or spatula to gently fold the cereal into the marshmallow-peanut butter mixture until all the rice cereal is evenly coated. Be careful not to crush the cereal as you mix.
Once the cereal is well mixed in, fold in the Reeses Pieces. This will add a delightful crunch and bursts of chocolate throughout your treats.
Line your 9x13 inch baking pan with parchment paper for easy removal, if desired. Transfer the mixture into the pan and use a spatula or your hands (dampened, so it doesn’t stick) to press the mixture evenly into the pan. Make sure to press firmly to compact the mixture, but do not over-compress it, as you want the treats to remain chewy.
Allow the treats to cool completely at room temperature. Once set, use a sharp knife to cut them into squares or rectangles. Serve immediately or store for later!
