Line a 9x13-inch baking pan with parchment paper.TIP - If you don’t have parchment paper to line the baking pan, you can also grease the pan with butter (having the parchment paper makes for slightly easier removal)
Cut butter into quarters and place in a large pot over medium heat.
1/2 cup unsalted butter
Once the butter starts to foam, reduce the heat to low and add the peanut butter and vanilla extract. Stirring until smooth.
1 cup creamy peanut butter, 2 teaspoons pure vanilla extract
Add the mini marshmallows and stir continuously until they are melted and no white streaks remain.TIP - Be careful not to burn the marshmallow mixture while melting it; it’s important to keep it at a low heat and stir continuously
20 ounces mini marshmallows
Pour in the Rice Krispies cereal, and, working quickly, stir until the cereal is coated in the marshmallow mixture. Be careful not to crush the cereal when stirring (I find using a soft silicone spatula avoids this).
10 cups Rice Krispies cereal
Transfer the mixture to the prepared baking pan and spread it into an even layer, making sure to reach the corners.
Allow to set for 30 minutes and then slice into 24 equal servings.
You can use any peanut butter, as long as it is not crunchy-style, as this will affect the overall texture of the treats.
Mini marshmallows melt more easily, but you can swap them with regular-sized marshmallows if that's what you have on hand. I would recommend chopping full-sized marshmallows up to help them melt quickly.
To avoid hard or overly dense treats, only lightly press the mixture down in the pan. If you press them too hard into the pan you are eliminating all the air and condensing them too much. Also, do not refrigerate the finished treats; doing so will make them hard.