Grease an extra-large mixing bowl, a 9x13-inch pan, and a silicone spatula or wooden spoon with butter or baking spray.
Pour the cereal into the bowl and set aside.
Bring the corn syrup to a boil over medium heat. Let it boil for 90 seconds.
Remove the pan from the heat and let it sit for one minute before stirring in the peanut butter.
Add 1 cup of the marshmallow fluff and stir until blended.
Pour the mixture over the bowl of cereal.
Spoon the remaining marshmallow fluff on top.
Stir until combined with a few streaks of marshmallows not mixed in.
Pour into a buttered 9x13-inch pan. Spread into an even layer.
Heat the peanut butter chips and 2 tablespoons of peanut butter in a small bowl in the microwave for 20-second bursts of high power, stirring after each, until melted.
Pour the peanut butter topping into a zip-top bag and snip off one tip. Drizzle it over top of the Rice Krispie Treats.
Set aside to cool for at least 2 hours. Then cut into 16 rectangles or 24 squares.
Notes
Store your Fluffernutter Rice Krispie Treats in an airtight container for up to 7 days or package them in zip-top bags and freeze them for up to 3 months. Thaw them in the bag at room temperature for a few hours before removing the treats from the bag.