Lightly grease a 9x9-inch baking dish with butter or non-stick spray, or line it with parchment paper for easy removal.

In a large pot, melt the butter and peanut butter over low heat. Once melted, add the mini marshmallows and stir constantly until they’re completely melted and smooth.

Remove the pot from heat and quickly stir in the vanilla extract until well combined.

Add the Reese’s Puffs cereal to the melted marshmallow mixture.

Stir gently until all the cereal is coated evenly with the marshmallow mixture.

Pour the cereal mixture into the prepared baking dish.

Using a spatula or lightly greased hands, press the mixture firmly and evenly into the pan.

If you’re adding mini chocolate chips, sprinkle them evenly over the top of the bars and gently press them down so they stick.

Let the bars cool at room temperature for about an hour, or until they’re set.

Once cooled, cut into squares or bars and enjoy!