Prepare Brownies as instructed on box using a 9x13" pan.

Cool completely.

After they are cool, refrigerate for 1 hour.

Spread Marshmallow Fluff over the chilled brownies, creating an even layer of marshmallow.

Return to refrigerator for at least 30 minutes.

In a large microwave-safe bowl, pour the chocolate chips and the peanut butter.

Microwave 30 seconds then stir well. If it needs to melt more, microwave in 15 second intervals stirring in between.

Stir in the Rice Krispies.

Spread the Rice Krispies layer over the Marshmallow Fluff layer.

Return to refrigerator for at least another hour before cutting.

Store in the refrigerator in an air-tight container.