In a large saucepan, melt the butter over low heat. Add the mini marshmallows and stir constantly until the mixture becomes smooth and fully melted.

Remove from heat and fold in the Rice Krispies cereal until every piece is coated. Press the mixture evenly onto a greased or parchment-lined surface, shaping it into a thin rectangle.

In a microwave-safe bowl, combine the peanut butter and chocolate chips. Heat in 30-second bursts, stirring in between, until completely melted and smooth.

Spread the chocolate-peanut butter mixture evenly over the Rice Krispies rectangle.

Carefully roll the Rice Krispies layer into a tight log, starting from one short edge, using the parchment to help guide it.

Wrap the roll in the parchment and chill in the refrigerator for at least 1 hour, or until firm.

Slice into 1-inch rounds and enjoy, either chilled or at room temperature.